lodgment within the tube from which it had some time before escaped, by means of repeated dives towards the hitherto open end, which has since become closed. I have observed such struggles continue for a minute or more, but never with the success apparently desired. Many months since I mentioned at one of the meetings of the Lyceum of Natural History in New York, that I had seen two apparently different genera of diatoms existing within the same investing tube; and now I wish to place that fact upon record, and state one or two more instances of the same mode of growth. During the month of March, 1868, I found in the harbour of New York specimens of Schizonema Grevillei in active motion within their investing tubes, but accompanied by a much smaller form possessing a totally different outline from S. Grevillei, being blunter at the ends, and with parallel sides on S. V. During the same month, and also in April, I found this mode of occurrence very common, and also Schizonema Grevillei and a Homeocladia in the same tube, and Schizonema cruciger and the small form mentioned above, both in the same tube, and S. cruciger and Grevillei in the same tube. In all these cases the frustules were in lively motion, passing over each other from one end to the other of the tube. In May of the present year (1869), I found growing in the salt water of the "Mill pond" at Salem, Mass., Schizonema cruciger and Nitzschia closterium, W. S. (Ceratoneis closterium, C. G. E., and Nitzschiella closterium, L. R.), both in the same tube. And here it will be necessary to say something in regard to the form I have called Nitzschia closterium, as I shall thereby, I hope, be enabled to clear away a little fog of synonyms. Neither Smith, Kützing, nor Rabenhorst describes or figures any species living within a tube like Schizonema, the frustules of which have an outline and markings similar to Nitzschia closterium, so that it is not likely that they ever saw anything but the free form or condition of this species. However, Ehrenberg figures and describes, under the designation of Schizonema? Agardhii (Die Infusionstheirchen, 1838, p. 343, T. xx., fig. xvi.), a form agreeing with this, but the structure of the frustule is that of Nitzschiella of Rabenhorst, so that the specific name of this species should be Agardhii, whatever its genus be decided to be hereafter. For the present, as it is nearest allied to the forms grouped under Homeocladia, it had better be placed in that genus, so that the synonomy would stand thus: Homeocladia Agardhii, C. G. E. (sp.). Abhand. K. Akad, Berlin. P. 311. 1833. 1840. 1853. 1864. Ceratoneis closterium, C. G. E. facts as these I record, as well as that of which I sent an account, and illustrating specimens to the late Dr. Walker-Arnott-and which has been noticed by Mr. F. Kitton, who examined my specimens, in 'Hardwicke's Science Gossip' for May, 1869*-of the occurrence of what are usually considered two distinct species of Gomphonema, viz. G. capitatum and G. constrictum, both growing upon the same stipes or stalk! But this is not all. Since then I have made gatherings at the same place, and still find the above two forms growing upon the same stalk, and two others of totally different outline which appear also upon the same stipes. So that here we would have four hitherto considered distinct species arising from the same individual. I do not name the two last-mentioned forms, as I am in some doubt with regard to the names that have been applied to them. The question of what is the individual in the Diatomaceæ is again raised by the observance of these facts, as well as those I described in my "Note on a point in the habits of the Diatomaceæ and Desmidiaceæ," read before the Boston Society of Natural History, January 8, 1868, and published in their 'Proceedings.' The specimens illustrating the remarkable mode of occurrence of the two forms of Gomphonema which I sent to Dr. Arnott unfortunately did not arrive until after his death; but, speaking of my having so found them, he wrote to me in the last letter I received from him as follows. I feel that I am justified in publishing this extract, as it is of such importance; and I also know, from what he wrote to me, that he himself would not object to my doing so were he still living. "Your discovery of Gomphonema constrictum and capitatum growing on the same stalk is interesting, if you are not deceived. When a Gomphonema spore grows on a weed, the stalk (which is merely the external mucus collected at the one end) is formed by the growing frustule. It is not the stalk (or in Schizonema, the tube) which produces the frustule, but the frustule which produces the stalk or tube. Then when the frustule self-divides, several are formed, either side by side, or each may project a new stalk; but seldom with much regularity. Now every frustule and valve arising from the same spore must be precisely alike, being all formed from the original frustule by repeated self-division; and as selfdivision merely repeats the same identical form or variety, it is not easy to understand how it is possible to have two varieties of form on the same stipes. If there be no mistake on your part, you will overturn all the present views of the production of new frustules and valves. It is more easy to suppose that a frustule from another stipes had become agglutinated to the stipes. But as you say you have sent some in a bottle, I will examine it with care when it arrives. Every spore may produce a different variety, but it is not easy to understand that the same spore, or stipes, can give rise to * Vol. v., p. 109. † Vol. xi., p. 361. different varieties. As for the two species (G. constrictum and capitatum) I have never been satisfied that they are distinct, and probably G. herculaneum is another variety." For my part, from the mode in which the two new valves are formed within and between the two old ones, when self-division takes place, I can readily understand how a great variation in both outline and sculpture can occur. In this case the two forms have exactly the same sculpture, and the difference between them merely lies in the outline of the valve. From my knowledge of how greatly this character varies in the Diatomaceæ, I, from an early period in my studies, considered these two supposed species to be but forms of one, and this discovery proves that my surmises were correct. At some future time I may have something to say with regard to the genus Gomphonema, and what, in my judgment, constitutes a species in it. I am now engaged, and have been for some years, working up several genera, with the express purpose of determining the true lines of specific distinction in them. And I must be permitted to here enter my earnest protest against the custom which has become so wofully common, in England more especially, of manufacturing species where they do not exist. The labours of such self-supposed students of nature are more than thrown away. Our books become crowded with worthless synonyms, and this branch of biology has, in consequence, fallen into disrepute among scientific observers generally. If those who have the opportunity of securing and examining specimens of Diatomaceæ, would only study them a little more carefully, and if they must publish, do so only after properly maturing their knowledge, we might hope to learn something of the life history of these strange atomies. Better that really new species should for ever remain unnamed, than that such contributions to the literature of the Diatomaceæ, as appear from time to time in foreign journals, should ever see the light. It is a curious fact that almost everyone who becomes possessed of a microscope of sufficiently high magnifying power, at once imagines that he is abundantly armed and equipped, as well as qualified, to attack and overcome the most difficult problems in biology. Hence we find the most startling discoveries put forth by very immature observers of nature, who suppose themselves to be students, but who have really given little time or thought to study. No branch of biology, perhaps, has been more cursed with supposed discoverers of this class than the Diatomaceæ, until a man comes to be appreciated by the number of species he can manufacture. By far the largest number of observers who are attracted to these beautiful and wonderful atomies forget that we have in them presented to us for investigation one of the most puzzling problems in the whole group of phenomena, illustrating that which we call life; but, on the contrary, appear to consider them as "simple organisms," whose morphology and life history, as well as classification, are therefore proportionally easy of comprehension. I have devoted many years to the earnest study, under varying conditions, of these examples of complex simplicity, and pity it is that others who have not spent so much time over this branch of organic existence should not have been so fortunate as I was in possessing a wise and patient counsellor in the late Dr. Walker-Arnott. I can truly say that had it not been for his invaluable friendly advice, I too would have doubtless ranged myself with the manufacturers of species and synonym accumulators. Often have the kindly words he has written me made me pause ere I, as he pithily remarked, “rushed into print" with supposed discoveries, which I would have been ashamed of thereafter. Dr. Arnott says, "a microscopist looks on everything as subservient to the microscope, and that whatever he sees, and which appears distinct to the eye, he thinks ought to be described or figured as distinct. I am, on the other hand, a naturalist, a botanist in particular, and use the microscope, simple or compound, as a necessary evil, merely to enable my eyes to see better minute structures; but whether these differences amount to specific or generic importance, or are only peculiar forms of one species, is the result of analogy, a mental process which can only be attained by a training in botany in all its branches, for many years." Natural objects, like the Diatomacea, which can only be seen after they are magnified several thousand times, and then only under peculiar circumstances of illumination, must be difficult of comprehension, even if their life history were much more simple and more easily studied than it is. I cannot too strongly caution the intending student of this enticing branch against trusting to a few and hasty observations made upon the dead skeleton of the plant. It is only when they are studied in the living state that the Diatomacea can be understood, and even then only with difficulty. But one more abstract from my note book and I must draw these remarks to a close. In the early part of November, 1868, I made a collection of Colletonema vulgare, and for some time have been able to keep it alive in a bottle so as to study its peculiarities. And here let me say that many minute forms of both animal and vegetable life which I have been unable to rear otherwise, I have found to flourish in phials with small necks, or those with large ones which have the aperture partly stopped with a loose cover of some kind. It would seem that the gases given off from the human body, and accumulating in dwelling rooms, in which I have kept specimens, are deleterious to these small forms, and the partial closing of the vessel prevents, to a great extent, their entrance. My specimens of Colletonema flourished finely and grew considerably. I have been thus enabled to watch them, as I may say, building their Journal, July 1, 1870. tubes; this species, consisting of naviculiform frustules enclosed and freely swimming about in tubes, after the manner of Schizonema. In fact there is nothing to separate these genera, except that the first inhabits fresh water, whilst the latter is an inhabitant of the sea, where it is to be found generally in profusion, covering larger algae and rocks. The extension of the tube takes place after the following manner. As the frustules increase by the process of subdivision common to all of the Diatomaceæ, of course the two frustules thus formed occupy double the space of one, and as the cell division is continually going on, after a time the tube must become choked with individuals. At this period in their existence they appear to be extremely active, moving with increased rapidity up and down the tube as freely as their crowded condition will permit. Whether the end of the tube is never closed, or opens at certain seasons, I have been unable to determine; at all events it is now found to be open, and the frustules slip over each other until they reach this opening, and one or two will project outside as if prospecting, and will occasionally return within the general envelope. When a frustule thus projects from the open end of the tube, it never, as far as I have seen, rushes onward with the vigorous motion with which it moves within the envelope, but this is doubtless only so when the tube is being lengthened. It can be easily understood that if the species be disseminated by the distribution of perfect frustules, as seems to be most likely, that they must then escape from the tube after the manner I have recorded above as taking place in the allied genus, Schizonema. When one or two frustules have projected from the open end of the tube, they often immediately come to a rest just beyond the tube, or do so after moving over each other slowly outside of, but in a line with, the tube. While at rest there appears to form around them a transparent mucous sheath, which, so that it may not fix them in their position, is kept in a tube form by the frustules again moving over each other, and thus, as it were, fashioning and smoothing the inside of the tube. This sheath becomes more and more dense, until it is plainly visible as forming an elongation of the tube, when the frustules again project from the end, and a new portion is added. I have in this way seen a tube grow across the field of the microscope, and the closely-packed frustules extend themselves in single file, each just overlapping those in front and behind it. The membrane constituting the tube, although dense and strong, is somewhat elastic, but not very much so, for I have seen three or four frustules become wedged together by one attempting to pass backwards whilst the others were moving forwards, and at such times the tube does not stretch to accommodate the crowding, but yet is often bent by the force of the moving frustules. In fact this force must be considerable, as is evidenced by the size of the obstacles, as grains of |