age examples from the largest sub-maxillary row measured .or in height by half that width. I found no projecting filament, however, in any of the cups, such as is described and figured by Professor Wyman in the papers of Mr. Putnam already cited. The interior structure of the papillæ also differs greatly from that of Amblyopsis, as the latter is represented by Professor Wyman. In Amblyopsis, according to that eminent anatomist, each papilla is supplied with a nerve fiber which terminates in a short, flexible filament springing from the middle of the concavity in the tip of the papilla. In the Chologaster each papilla is likewise penetrated by a nerve fiber, which is very easily traced, even without the help of reagents, because of the black pigment in the neurilemma, but this nerve passes to an epidermal "end organ" precisely similar in structure to those minute bodies found abundantly embedded in the skin of the head of young fishes, and belonging to the same general class as those sensory structures which occupy the lateral line.

This "end organ," or "nerve button," which fills the interior of the distal third or half of the papilla, is a nearly globular mass of cells, partly various modifications of the columnar, and partly spindle-shaped or spherical, each of the latter with a filamentous prolongation at one or both ends. The nerve fiber of the papilla passes, without division, to the inner end of the cell-cluster, where its fibrils appear to continue into the filamentous processes of the cells. Having no fresh material for the osmic acid treatment, I could not positively demonstrate the terminations of the fibrils. These are evidently simple examples of that class of structures to which a supposed "sixth sense" of fishes and amphibians has been assigned, and by which these animals are believed to appreciate motions of the water and wave lengths longer than those of sound.

The importance of well developed structures of this character to fishes without the use of the sense of sight, is very manifest. The close general resemblance between these organs and those described for the blind fishes, taken in connection with their similar situation, arrangement and apparent use, is probably sufficient evidence that the two kinds are homologous.1

1 Is it not possible that the specimens of Amblyopsis studied by Professor Wyman were not perfectly preserved, and had lost more or less of their superficial epithelium, and with this the "nerve buttons" from the tips of their papillæ? Some color

Recurring now to the argument of Mr. Putnam, we note that the discovery of a species of Chologaster which frequents external waters of an immediately subterranean origin, supplies all needed proof that the genus either has a shorter subterranean history than Amblyopsis, or, at any rate, has remained less closely confined to subterranean situations; and that in either case the occurrence of eyes, partial absence of sensory papillæ and persistence of color, are thus accounted for consistently with the doctrine of "descent with modification."

The extraordinary development, in only a part of the genus, of a special sensory apparatus peculiarly useful to a fish unable, for any cause, to see, points the same way, and gives evidence of a progressing adaptation of these fishes to their unusual abode.

The intermediate relation of the sensory tubercles of Chologaster to the much smaller ones of young fishes and the permanent papillæ of Amblyopsis, points out the evident origin of the last through the permanency and higher evolution of structures. commonly evanescent in the young.

is given to this surmise by the statement, in the papers cited, that his fishes were pro. vided with only a single layer of delicate epithelium; whereas most fishes, and especially the naked and nearly naked kinds, are usually covered with an epidermis several layers deep, and by the further fact that the papillae of Chologaster would ac curately resemble those figured in Mr. Putnam's paper (except for the filament), if the former were denuded, as supposed.

After the above was sent to the printers, Mr. Putnam kindly sent me an alcoholic specimen of Amblyopsis with the epidermis intact over considerable areas of the head. An examination of the sensory structures of these regions at once showed the correctness of my surmise, that they are in Amblyopsis, as in the new Chologaster, to be definitely classed with the so-called "organs of the sixth sense," and are simply more highly developed examples of the structures found in the heads of young fishes. Each papilla bears at its tip a cluster of sensory cells in all respects similar to those above described; and I have little doubt that the figures of Prof. Wyman were made from denuded papillæ which had accidentally lost their sensory cells. The "filaments" seen by him on two or three of the papilla were probably remnants of the cell clusters. The epidermis of the head is not composed of a single layer of delicate cells, as described by him, but of at least three layers-a deeper, columnar one, a median layer of large spherical or oval cells, with granular contents, and a superficial layer of thin, flat cells. The epidermis is, in fact, so thick that it almost or quite conceals the folds of the true skin upon which the papillæ are borne. A fuller account of these structures will be given in another article.

A SINGULAR PARASITIC ISOPOD CRUSTACEAN AND SOME OF ITS DEVELOPMENTAL STAGES.1

THE

BY CARL F. GISSLER, PH.D.

HE material for the present paper was obtained from the common prawn of our shores, Palamonetes vulgaris Stimpson,* about ten per cent. of which I found infested, in June, 1881, with a Bopyrus (Bopyrus palæmoneticola Packard3), probably the same species which Professor Joseph Leidy mentioned as occurring near Atlantic city, N. J. The female of our Bopyrus averages in size from 3.50 to 4.50mm in length, and 3 to 4mm in width. Its ventral side is invariably turned toward the carapace of the prawn and its marsupium or breeding cavity is usually filled

FIG. 1.-The common prawn (Palamonetes vulgaris Stm.) with its parasite. Natural size.

with minute yellowish eggs of a nearly spherical form. From three hundred to three hundred and fifty eggs are contained in this cavity; the latter being formed by the prolonged lamellate margins of the thoracic segments.

The body of the female is of a whitish color, and as in all

1 Jenaische Zeitschrift für Medicin und Naturwissenschaften, Vol. vi, 1, p. 53, 1870. Dr. Fritz Müller. (Bopyrus and Cryptoniscus.)

2 Read before the 30th meeting of the A. A. A. S., August, 1881. In this paper the Bopyrus was provisionally called B. manhattensis.

3 See also my note in Scientific American, Vol. XLI, No. 10, September 3d, 1881. Annals Lyceum Nat. Hist. N. York, Vol. x, p. 129, 1871.

5 Zoology for High Schools and Colleges. By A. S. Packard, Jr., M.D., Ph.D. 1881, 3d ed.

6 Proceedings Academy of Nat. Sciences, 1879. See also Report on the marine Isopoda of New England. By Professor Oscar Harger. p. 312.

members of this family, is somewhat distorted and unsymmetrical, one side having narrower segments than the other, and is therefore of a triangular shape.

Degeneration as a result of parasitism is manifested in the absence of eyes as well as antennæ proper, in the clumsy form of the feet and the much reduced mouth-parts. The head evidently consists of two unequal fleshy lobes. The dorsal cephalic lobe is triangular and somewhat unsymmetrically placed, the ventral lobe is of subquadrate shape, anterior angles produced, posterior angles rounded, with the middle of its posterior part prolonged. and rounded.

Of the mouth parts I was unable to find more than one pair of maxillæ inserted at the sides of the ventral cephalic lobe. They constitute a flat, roundish, terminal piece, the palpus, with nine marginal hyaline tentacles; the basal joint is connate with and obliquely inserted into the median lobe. A number of musclenerves (muscle and nerve together) run to the tip of the basal maxillary joint, some of which enter the palpus, others (three) distribute themselves along the outer tip of the former, entering three longer and stouter marginal tentacles. A beautiful dendritic arrangement of black pigment is found near the base of the palpus.

From underneath the body of the ventral cephalic lobe arise a number of narrow, ligulate, gill-like appendages, which are, in the live animal, kept in constant rapid paddling motion. Viewed under higher microscopic power, they exhibit a granular structure with longitudinal, hyaline, evidently lacunary canals. If it was not for their abnormal position near the anterior part of the body and their structure, I should regard them as gills, but to be consistent, am obliged to see in them paddling organs for the purpose of aërating the eggs or embryos contained in the marsupium.

The seven pair of feet are curved forward and downward, and terminate in an indistinct hook-like knob. The black pigment is very irregularly distributed in the feet, some are all yellowish, others but slightly pigmented, and again others are nearly all black. This I have observed in live specimens, and it seemed to Compare with C. Spence Bate and J. O. Westwood's History of the British sessile-eyed Crustacea, Vol. II, p. 218, fig. 9.

1C. Spence Bate and J. O. Westwood, op. citat. p. 220. two or three membraneous, flattened, pointed appendages.

*

*

*furnished with

me that, when black, the pigment is centrally located in the legs. The thoracic segments have, as apparently in all Bopyridæ, their margins prolonged into more or less lanceolate pigmented lamellæ. To these lamellæ the feet are attached. The lamellæ attached to the first pair of feet is a small, beautifully pigmented oval lobe, and its entire margin is fringed with delicate tentacles. The second and third pair of feet have very broad lamellæ, with forward directed sub-ovate tip, and with their anterior margins fringed. The fourth, fifth and sixth pair of foot-lamellæ are short, broad and irregularly triangular pieces; seventh lamella very long, narrow, lanceolate.

The marsupium is an open, roundish cavity, surrounded by the above-mentioned lamellæ, and covered by the carapace of the

prawn.

The abdomen is deeply segmented, and ventrally provided with roundish appendages overlapping each other in the median line. I have closely observed the live females, and doubt that those abdominal appendages functionate as gills. They consist of a larger thick fleshy lobe, and a smaller, still thicker roundish piece. They are the degenerate postabdominal legs, characteristic of the order of Isopoda. Usually four, but sometimes six pairs of the thoracic epimera are more or less black pigmented.

The male averages about Im in length by 0.25mm in width. Head with a pair of lateral pigment eyes. Head and seven thoracic segments black pigmented, the pigment exhibiting, beside the ordinary form, a pretty stellar arrangement.

Anterior angles of thoracic segments oblique, abdominal segments four, pale, their margins perfectly round, segments gradually becoming narrower toward the terminal median piece, which is minute, and, on treating with acetic acid, is seen to consist of two lobes.

The last of the thoracic segments, not being as fully pigmented. as all the preceding, exhibits dorsally a twisted, serpentiform (bretzel-shaped) marginal ornamentation.1 Eight pairs of legs with powerful claws. Antennæ apparently two-jointed, first joint club-shaped, with five minute bacilli on its tip, second joint much. narrower, about one-quarter as long as the first, with six bacilli at its tip.

1 Similar to the male of Cepon distortus Leidy, Journ. Acad. Nat. Sc. Phila., Vol. III, 2d series, 1855 to 1858, Piate x1, Figs. 26 to 32.