and I take the opportunity so offered of putting my observations upon record, so as to facilitate future studies by others.

Graff says the capsules observed by him in material supplied from the Frankfurt a. M. Aquarium, by Dr. Schmidt, measured about three millimeters long by one and a half wide, which would correspond pretty nearly with the outline of the largest capsule observed by me and represented in Fig. 9. But according to him these large capsules contained from two to nine embryos, while those observed by me never contained more than one, the presumption, therefore, is, that they belong to distinct species, and that on this specimen of Limulus, Planaria limuli was not present.

All of the capsules were apparently chitinous, and attached by a cylindrical stalk to the surface of the branchial leaflets by a disk-like expansion of the end of the stalk, as represented in

Capsules and Embryos of the Planaria of the Horse-shoe Crab; enlarged. Figs. 1-7 and 9. In form the capsules are oval and flattened, lying down flat against the surface of the branchial leaflets with the plane side. The lower side of the capsule is flat, the upper convex, as shown in a side view, Fig. 4. When the young escape they find their way out by the free end of the capsule, which is ruptured as represented in Fig. 7. They are scattered all over the branchial leaflets and on both sides of them. The different sizes were often seen side by side on the same leaflets together with the parent worms, which, as Graff observes, had often eaten through the branchial structures. So extensive was this damage that I suspect they cannot be considered merely as commensals, but rather as true parasites, for it was frequently observed that four or five successive leaflets were eaten through in the vicinity of a large adult worm, so as to produce large irregular perforations with evidences of degeneration of the branchial tissues at the margins of the openings. That they should find it easy to feed off of their host is not to be wondered at, in that the branchial leaflets are composed of two very thin chitinous lamella which are kept apart by numerous rounded pillars; in the space between the lamellæ and around the supporting pillars the blood of the host circulates. In consequence of this arrangement, all that

our parasites need to do in order to get at the juices of their host, is to cut through the lamella next to them and they have an abundant supply of food always at hand. It appears that Van Beneden, the elder, regards them, on the authority of A. Agassiz, as messmates, but from the foregoing recital it would appear that they are more or less truly parasitic in habit. It appears that other crustaceans are infested by planarians, and Professor Leidy has described a parasitic genus, Bdellura.

On the specimen of Limulus examined by me there were three well-marked types of egg capsules. The first, represented in Figs. 1-4, enlarged sixteen times, measured about a twelfth of an inch, or about a line, in length, and usually contained from two to four embryos. The branches of the gastric cavity are separate posteriorly in the embryos, but afterward become joined, as shown in Fig. 10, supposed to be the adult of this second form This form has a pair of eye spots developed at a very early period

10

Parasite of the Horse-shoe Crab; enlarged.

which are retained when hatched. The mode of segmentation of the eggs is very difficult to make out in the capsules, as the individual ova are very strongly pigmented, and consequently almost opaque, so that the contours of the cells cannot be discerned,

The second form, represented in Figs. 5-7, enlarged sixteen times, is much smaller but similar in structural features to the preceding. The capsules measure about one-twenty-fifth of an inch in length, and contain usually two eggs or embryos. At first the ova occupy each one of the ends of the capsule, as shown in Fig. 5, but after the young worms have developed somewhat they usually lie along side of each other lengthwise of the capsule. They frequently change positions, however, at this

stage, and it sometimes happens that there is but one embryo in a capsule. The ova of this, like the preceding species are nearly opaque, and the walls of the stomach in like manner are composed of very dark granular protoplasm.

The next form of capsule observed, is that represented in Fig. 9, enlarged sixteen times, and is supposed to belong to the adult represented in Fig. 8, enlarged five and a half times. These, as stated before, were never seen to contain more than one embryo, and measure over an eighth of an inch in length. The egg is not so darkly pigmented as in the other forms. The supposed adult of this species, Fig. 8, is apparently without eyes, and the cæcal diverticula of the stomach are arranged in a paired system on either side of the median line independent of each other. The peculiar hood-like cephalic extremity may be of the nature of a sucking disk. This last form is milky white in appearance; the cæcal prolongations of the stomach, yellowish. The stomach in the other forms is dark brown, so that the two types of forms may be at once distinguished.

I do not propose to name the species, as these supposed distinct life histories may, after all our endeavors to separate them, be only phases of the same thing. Sure points of distinction can only be got by a more thorough study of these interesting types than I have been able to bestow upon them, and I leave them here in the hands of such helminthologists as may be disposed to give the subjects of this notice further attention.

I have not seen Dr. Graff's final piper, in which P. limuli was to be fully described and illustrated.-John A. Ryder.

THE CIRCULATION OF SESSILE-EYED CRUSTACEA. - Dr. Yves Delage has published in the Archives de Zoologie expérimentale et générale, a superbly illustrated and detailed memoir on the circulation of the sessile-eyed Crustacea. The plates are printed in colors, so as to bring out clearly the heart, arteries, venous sinuses and veins; moreover, sections of the body are given, so that the topography of the circulatory system is given in a graphic manner. The memoir is too long for abstract, but it is one of the most valuable contributions of the past year to our knowledge of the Crustacea. The circulation appears to be on much the same plan as in the Decapods.

VIVIPAROUS CHIRODOTA.-A Brazilian species of this genus of Holothurians, or sea-cucumbers, has been found by Professor H. Ludwig to be viviparous. The genital tubes appear to give rise to both eggs and spermatozoa, the latter being developed in their blind ends and lateral bunches. The young to the number of sixteen, and all of the same stage of development, were found lying freely in the body-cavity. They had seven tentacles, two of them minute, and in the body-wall were groups of developing or developed calcareous wheels.

A MARINE PLANARIAN AND ITS HABITATION.-In June, 1881, a very large female specimen of the common horse-shoe crab (Limulus polyphemus) came into my hands,' on the gills of which I observed a number of brown small bodies like seeds of some plant, together with living whitish worms, a dendrocœlous Planarian, the Bdelloura candida Girard.

These worms were of various sizes, the largest (Fig. 1; side), measuring 16mm in length and about 6mm in width, by about 1mm in thickness. They moved slowly and snail-like over the large lamellous gills, their body-margin, especially the anterior portion, having undulating motions, these being respiratory movements. On placing them in alcohol they became considerably wrinkled

and contracted. The larger ones had neither cephalic notches (which occur in some members of this family), nor eye-dots. The dorsal side showed a faint line running along and close to the entire margin. A large round muscular bag occasionally protruded from a little behind the middle of the ventral surface; this is the pharynx.

In alcoholic specimens a second roundish smaller opening could be seen a little behind the pharynx, the genital orifice. The alimentary system had about ten or eleven lateral sacs.

The seed-like brown bodies found together with the Planarians, I immediately took for their egg-cases, which proved to FIG. 1.-Young Planaria, be correct upon opening some of them 3mm long, extended. oc, whence one or two young Planarians could eyes; i, alimentary system be taken. They were of a cream color and

rynx opening; g, male more transparent than their parents. But genital glands: g, genital strange enough, they had a pair of distinct orifice. Figure at the side represents size and form eye-dots, which, I presume, in the adult of an adult Planaria. have degenerated.

The pharynx, the genital orifice and even the genital gland (Fig. 1 g) could be recognized. From analogy, I infer the latter to be the male organs, the female glands having escaped my observation, since our worm is hermaphroditic. The movements of these young worms were more rapid than in the older ones.

The egg cases were of various sizes, by far the greatest number, however, being 3.50mm in length (excluding the stem), by 1.50mm in width. They were plano-convex, the latter exteriorly, the former towards the gills. They consisted of a brown, homo

1 From Theo. C. Hepp, M.D., Brooklyn, N. Y.

2 Identified by Professor A. S. Packard, Jr.

In alcoholic specimens in every case.

geneous, thick and leathery mass, either ovoid or cup-shaped, some of them having a sort of a lid on their tip.

Within many of them were the young Planarians, free, moving about, from one to three individuals

d

in each capsule, in others the same were again enclosed within a similar ova! case without stem, and again a others were found with their tip broken off and empty. The greater number of them were covered around their tip with bluish (colorless in FIG. 2.a, egg capsule with a alcoholic specimens) ten-pin-shaped lid, enclosing two encased embryos; tubes with open tips. As these egg-capsule with one free young enclosed, capsule with air-tubes (?) tubes were invariably on or near the arounl tip; c, ordinary form of tip of the capsules only, they cannot egg-capsule, enclosing three young be taken for parasitic organisms, but Planarians; d, empty egg-capsule with three empty cases near orifice. may presumably be openings for an exchange of oxygenized water for the enclosed offspring. Those capsules having no such tubes, probably got them rubbed off through the motions of the gills of the Limulus. A few specimens of this Planarian, from three to five millimeters in length, the size usually found only within the capsules, were amongst the larger ones creeping around. These must have just left their protecting homes.-Carl F. Gissler, Ph.D.

EYE OF PLANARIANS.-Professor R. Hertwig finds that the nervous system of these worms is very primitive in character, and is but slightly separated off from the surrounding tissue; in the eye it is possible to distinguish a black pigmented and a clear colorless portion. The former lies along the animal's axis; the latter is just below the epithelium, and is only separated from it by the basal membrane. The pigmented portion, again, consists of two parts, a transparent nucleus (vitreous body) and a superficial layer of surrounding pigment cells, which are only wanting at the diaphragm-like point at which the retina or colorless part is connected with the rest. The cylindrical fibers of the vitreous body are arranged parallel to one another, the nucleated ends being nearest the pigment. The retina is only formed of optic cells, which are continued at one end into a nerve-fiber, and at the other into a rod-like process. The fibers of the optic nerve traverse the retina in a very irregular manner, so that there is no regular arrangement of the optic cells.

THE STRUCTURE AND AFFINITIES OF THE HIPPOPOTAMUS.-In a recent illustrated paper, entitled "Observations upon the Hippopotamus," by Professor H. C. Chapman, published in the Proceedings of the Academy of Natural Sciences of Philadelphia, the author gives a résumé of what has been published upon the general anatomy of this animal, of which he dissected an adult male and female