PACKAKD.] MORPHOLOGY OF PHYLLOPODA. 383 



sense-filaments, or what we may call tlie olfactory filaments, are smaller 

 and less numerous than in L. gouldii. 



In Estlieria mexicana, Plate XXIX, fig. 1, la, 1&, the segments on 

 the anterior side are piu)duced into what may be called the olfactory tu- 

 bercles, which give a bluntly serrate outline to this side of the antenna 

 in contrast to the even opposite or inner side. In fig. 1, the antenna! 

 nerve {at. n.), where the sense cells and tubercles do not occur, is seen 

 passing through the middle of the antenna, and the ends of the fibers 

 disappear among the nerve cells, which crowd the olfactory tubercles 

 (fig. lb, ol.). In this species no olfactory filaments were observed to be 

 present. In Ustheria compleximanus however, Plate V, figs. 3, 4, they are 

 well developed, two or three, and sometimes more, short filaments arising 

 from the tubercles, which are more acute than in JE. mexicana (from 

 Kansas). The structure of the olfactory papillae {pi, paj).) is nearly 

 identical with those of lAmnetis. The ultimate fibers of the olfactory 

 nerves are here plainly seen to enter the mass of nerve cells. 



In Limnadia texana, Plate XXVI, fig. 3, the joints of the antennse 

 are more richly charged with nerve cells, which are rather smaller than 

 in Estlieria compleximanus, though those of the latter species are larger 

 than in E. mexicana. The histological structure of the first antennse in the 

 present family is quite unlike that of the same appendages in the Apodidm 

 and Branchipodidw ; and reasoning by exclusion, and taking into account 

 the fact that this pair of antenups do not project much beyond the edges 

 of the valves, and that they are placed very near the jaws and mouth- 

 opening, and also bearing in mind the great abundance of the sense- 

 cells, we are inclined to believe them to be either olfactory or gustatory 

 in function, and that in this family at least the first antennae are mainly 

 organs of smell or taste. We have often observed Limnetis gouldii, swim- 

 ming quite rapidly on its back at the surface of the w^ater, apparently 

 feeding upon the vegetable matter floating on the surface ; during its 

 movements it would stoi^ and feed upon some object, as if arrested by 

 its smell. The sense lodged in these organs are therefore restricted 

 either to the sense of smell or taste, probably the former. 



The finer structure of the antennas of Apus has not been examined, 

 and it is probable in an indifferent state. That of the first antennae of 

 Branchipodido} is quite simijle. Plate XXIX, fig. 6, represents the first 

 antenna of BrancJiipus vernalis greatly enlarged. It is simpler in struc- 

 ture than in the European B. stagnalis as figured by Leydig (Sieb. u. 

 Koll. Zeits. Wiss. ZooL, iii, PI. VIII, fig. 8), since it lacks the series of 

 seven sense filaments ending in knobs of the European species, though 

 the three terminal setae are much longer. In our species the antennae 

 are seen to be unjointed throughout its whole length. Two nerves, one 

 on each side (fig. Qn), and composed of several fibers with here and 

 there a ganglion cell, approach each other in the middle o± the append- 

 age, where they are reinforced by a ganglion cell or two. At n' two 

 nerves are seen passing along the center of the appendage ; at ^ c are 

 situated several ganglion cells in the nerves, which finally lose them- 

 selves in a terminal mass of small compact ganglion cells, situated at 

 the base of the three setae. Leydig only figures five cells, where in B. 

 vernalis they are smaUer and much more numerous. It seems obvious 

 that in this family the first antennae only possess the sense of touch. 



On Plate XXXIV, fig. 4, Dr. Gissler has figured the first antenna 

 of the larva of iStreptocephalus texamis, from Kansas, and it will be seen 

 that the histological structure is rather different from that of the adult 

 Branchipus. The ganglion cells are more abundant at the base of the 

 antennae ; the nerve passes along the center, is reinforced by a few large 



