REVIEWS. * On an Undescribed Form of Amaba. UNDER the above title, Dr. G. C. Wallich has lately published some very interesting observations on "Amoebae, and allied forms of Rhizopoda," in the Annals of Natural History.' In certain ponds on Hampstead Heath he obtained a curious form of Amaba in considerable quantities, and is of opinion that the peculiar characters presented by them are normal, although, perhaps, not permanent in their nature. 'According to the descriptions of the commoner forms, such as A. princeps, A. diffluens, or A. radiosa (which he believes ultimately will be found to be mere transitory phases of one species), it appears that the sarcode-substance is uniformly differentiated into 'endosarc' and 'ectosarc'-in fact, neither the outer layer of sarcode nor the more viscid mass within is endowed with a more advanced degree of development at one point than at another." In the variety which Dr. Wallich describes this is not the case, one portion of the ectosarc in it exhibiting a structure differing permanently from the remainder, being densely studded with minute papillæ, "which," says Dr. Wallich, "in the quiescent state of the creature, are of nearly uniform aspect and size, and cause the surface upon which they occur to resemble the villous structure of mucous membrane in outward appearance. When the animal moves, these papillæ or villi vary in length, and now and then several coalesce, so as to form processes more nearly approaching the ordinary pseudopodial character, although still of minute proportions. The villous patch, which occupies probably from th toth of the entire superficies, appears frequently to be employed as a prehensile organ, the creature being enabled through its agency to secure for itself a continuous point d'appui, from which the rest of the body is pushed or flows onwards." True pseudopodia are not projected from this villous patch, but are freely thrown out from the remaining portion of ectosarc when *Annals and Magazine of Natural History' for April, May, and June, 1863. needful. The prehensile power of the papillæ is very great, so much so that when undue pressure has been exerted upon one of the Amoebæ it has been torn asunder, the portion provided with the villous area remaining attached to the glass slide on which it had been placed for observation. The great abundance of the Amoeba in question in the ferruginous ponds of Hampstead, more than 95 per cent. of all the specimens being furnished with papillæ, has induced Dr. Wallich to consider this as a distinct species, which he proposes to call Amaba villosa. He, however, admits at the same time the probability of all the species of Amœbæ being local forms of one and the same type. The largest specimen which Dr. Wallich observed was th of an inch in diameter. The villi, in their quiescent state, seem to be about 'ths of an inch in average length. In some instances the villous portion was placed on a long pedicle of ectosarc, so as to give it the appearance of a brush. In these specimens the villi seemed to have lost their prehensile power. In many cases an infundibuliform orifice was observed in the centre of the villous patch, from which numerous particles of matter were extruded, and also minute, perfectly formed Amabæ, which Dr. Wallich regards as a proof of viviparous parturition among Amœbæ. The orifice was only temporary, but recurred frequently in the same position in various specimens and at various times. Dr. Wallich's observations on the nucleus and contractile vesicle are extremely interesting, and of great importance. He says, "The nucleus consists of a pale, gray-coloured, spherical mass of granules, towards the centre of which may occasionally be detected a minute, clear nucleolus. It is contained within a hyaline and somewhat elongated vesicular cavity, but never occupies the entire area of the latter." This vesicular cavity is separable from the rest of the Amoeba, as a clear, membranous capsule, containing the granules of the nucleus. Dr. Carpenter and Mr. Carter have both spoken of the existence of a vesicular boundary to the nucleus, but they do not allude, Dr. Wallich believes, to the highly specialized membranous covering which is so remarkably manifest in A. villosa, and which seems to approach more nearly to the vesicle of the Gregarinide. Dr. Wallich assimilates it to the nucleus of Plagiocantha, Thalassicola, Acanthometra, and Dictyocha. The position of the nucleus in A. villosa is always, when at rest, in the vicinity of the villous patch. With regard to the contractile vesicle of Amoeba, Dr. Wallich is of opinion, from careful observation, that it is not formed by any definite wall, as Carpenter and Carter have described it. In A. villosa the con tractile vesicle appeared merely as an internal fissure in the sarcode-substance, and the existence of numerous vacuoles, which continually form and coalesce, or disappear, whilst under observation, seem to bear out this view of its nature. Dr. Wallich also confirms Mr. Carter's view, as opposed to that of Lachmann and others, that the contractile vesicle invariably discharges itself externally, the orifice being extemporised and of very minute proportion. On treatment with acetic acid and other reagents, no trace of a membranous envelopment to the sarcode-substance could be discovered, such as has been described by Auerbach in A. bilimbosa; but Dr. Wallich found that, by improper adjustment of the focus or want of proper illumination, the semblance of a double line, indicative of a true membrane, could be produced. He gives his conclusions on the relations between the ectosarc and endosarc in the following words :-"From these facts it is obvious that the ectosarc and endosarc are not permanent portions of the Protean structure, but mutually convertible one into the other; and that it is an essential feature of sarcode that, whilst the outer layer for the time being becomes, ipso facto, instantaneously differentiated into ectosarc, the same layer reverts to the condition of endosarc under the circumstances just described"-alluding to the formation of food-orifices. In the granular contents of the protoplasma, Dr. Wallich found numerous rhombohedral crystals, aboutth of an inch in length, probably of lime. Such crystals he has also observed in Euglypha, Arcella, and Acanthometra. As is well known, Professor Huxley observed prismatic crystals in Thalassicolla. Certain bodies, which Dr. Wallich terms "nucleated corpuscles" (probably identical with the discoid ovules of Carter), were also found; their function is, perhaps, connected with reproduction. Other corpuscles, larger and nucleated, about theth an inch in diameter, were met with. These he has termed sarcoblasts, and considers them allied to the "yellow bodies" of Foraminifera, Polycystina, Thalassicollidæ, &c. In soundings from the Atlantic bed Dr. Wallich met with minute discoidal structures (previously detected by Professor Huxley), which he termed coccospheres, and believed to be a step in the reproductive process of Foraminifera. He now thinks it highly probable that the sarcoblasts first become coccospheres, or something equivalent, and are then developed into the perfect animal. This subject, however, he is about to work out. Dr. Wallich's observations are of the greatest importance. The discovery of this new form of Amœba, with the peculiarities of structure it presents, places the Amabæ in general in quite a new light, assimilating them more closely to other non-Rhizopodal genera, such as Thalassicolla, Acanthometra, &c., and placing them, in Dr. Wallich's opinion, at the head of the Rhizopoda. On the Nervous System of the Nematoda. His THE nervous system of the Nematoda forms the subject of an interesting paper by Dr. Anton Schneider, whose previous contributions have contributed so largely to our knowledge of the anatomy of that class of worms. first paper, "On the Lateral Lines and Vascular System of the Nematoda," appeared in 1858,† and has been followed by two others in 1860-"On the Muscles and Nerves of the Nematoda," and "Remarks on Mermis."§ In his present communication he continues his observations on the nervous system, of which we proceed to give a brief abstract. A nervous system was described, in 1816, by Otto, in Strongylus gigas, but the first important contribution on the subject was by Meissner, in 1853-55, who described what he regarded as a complete system of nerves in Mermis albicans and nigrescens. This was followed up by Wedl and Walter in a detailed account of the same system in another species. But the supposed nerves of these authors were shown by Dr. Schneider in the latter two papers above cited to belong to the muscular system; and his views have since been adopted by Leydig.|| Even with respect to the central nervous system, Meissner's views were entirely upset, what he regarded as such having proved to be the esophagus. Dr. Schneider was unable also to confirm Walter's description of the central nervous system in Oxyuris ornata. The true constitution, therefore, of the nervous system in the Nematoda remained in considerable uncertainty. The only central organ that appeared likely to be such was a pale band lying on the œsophagus, first noticed by Licberkuhn, Wedl, and himself. Since that period, Dr. Schneider has kept the subject in constant view, and believes that he is now in a condition fully to describe both the central and peripheral nervous systems in the Nematoda. He attributes the success he has + Ibid., 1858, p. 426. Ibid., 1860, p. 224. Ibid., 1860, p. 243. || Ibid., 1861, p. 605. Archiv Anat.,' 1863, p. 1. met with to a mode of dissection peculiar to himself, and the Iwant of which (though extremely simple) has hitherto prevented the successful prosecution of the research. The central nervous system constitutes a ring closely surrounding the œsophagus, but not attached to it. On the other hand, it is firmly connected by various processes with the walls of the body. This arrangement suggested the mode of dissection to be followed for its due display, and which is thus described:-Cut off a portion of the anterior end of an Ascaris megalocephala, for example, about half an inch long; then, with a fine and sharp pair of scissors, slit up the walls of the body together with the oesophagus; then cut off the lips and remove the œsophagus, and spread out the walls of the body, and the central nervous system will be seen lying uninjured on their inner surface. The essential part of the proceeding is the slitting up of the œsophagus as well as the walls of the body. The preparation is much improved by the boiling of it for a short time in dilute acetic acid, after which the cuticle can be readily removed and the specimen rendered transparent by glycerine. Specimens of A. megalocephala not fully grown are better fitted for examination than older ones, owing to their greater transparency. This dissection affords the readiest and easiest view of the entire nervous system, but in order to learn its minute structure numerous transverse sections are requisite. These sections must be very carefully made with the sharpest possible knife. To allow of their being properly made, the worm must be hardened, first in spirit, and afterwards in chromic acid. Dr. Schneider's researches have been carried on chiefly in Ascaris megalocephala and Oxyuris curvula. In A. megalocephala the nerve-ring is placed about 2 mm. behind the oral orifice. From it six cords are given off in front; four of these (nervi submediani) arise nearly in the middle, between the border of one of the lateral intermuscular spaces and the middle line, though rather nearer the lateral space. The roots commence with a broad base, which gradually narrows into the slender cord. Two other nerves (n. laterales) lie in the middle of the lateral intermuscular spaces. These nerves are completely imbedded in the substance of the lateral space, and they may, with some pains and trouble, be at once dissected out, or may be seen more readily, but still distinctly, in simple transverse sections. Two strong nervous cords pass backwards; they arise on the ventral side of the ring, one on either side of the ventral line, towards which they tend in a sort of arch and are continued a short distance, but they cannot be traced beyond the arched anastomosis of |