1887.] NATURAL SCIENCES OF PHILADELPHIA. 307 



round nucleus and a quantity of dark pigment ; the upper and outer 

 halves being clear and transparent. In no case did I find the nuclei 

 in the clear outer portion, as figured by Seeliger (1. c. pi, xi, fig. 13). 

 These pigment cells are in their turn covered with a layer of colum- 

 nar cells, each of which contains a nucleus in its outer end. This 

 layer .does not seem continuous with the entodermal layer covering 

 the brain, and is probably a modified portion of the ectodermal layer 

 of the inner mantel. 1^ one or two specimens which I had prepared 

 without ascertaining their specific name, I found the eye to be much 

 more flattened than in the figure given here, and divided up into 

 several lobes. 



From the above description, Salpa would seem to possess a sort of 

 comi3ound eye. Passing out from the central fibrillar portion of 

 the brain, are several nerve trunks; from eleven to twenty-five 

 pairs, which show a clear enveloj)e with a dark granular axis. No 

 fibrils are to be seen. The brain is covered by the entoderm which 

 is, however, not in direct contact with it at all points. 



Below and anterior to the brain the entoderm of the median dorsal 

 surfiice is invaginated to form the Ciliated Sac, (I'hypophyse.) This 

 structure as seen in other Tunicates has iriven rise to much discussion 

 in regard to its function. Ussow^ and Julin''^ regard this as a gland, 

 Joliet^ considers it to be olfactory in character. In Salpa it consists 

 of a simple tube (fig. 13, rHy.) closed at the end next the ganglion 

 against which it rests, and opening at the other end into the branch- 

 ial sac. Its walls are made up of short thick columnar cells carry- 

 ing heavy cilia. It, however, possesses no such peculiarities as the 

 glandular coeca described in Ascidia mammillata. 



Lettering of Figures, PL XIII. 

 (6s) blood sinus. 

 {Br or br) branchia. 

 (cb) ciliated cushion (in gill). 

 {ebb) ciliated border band, 

 (ct) cuticle. 

 (coe) coecal appendages. 



1 Ussow: "Beitrage zur Kenntniss der Organization des Tunicaten." 

 Moscow, 1876. 



'^ Julin (Chas.): I'Hj'pophyse des Ascidiens in BlUI. Acad Sc. de Bel- 

 gique, 3d. Ser. T. 1. P. 2, p. 151. 



^ Joliet. M. L. : "Sur le developpement du ganglion et du "sac cilie" dan 

 le burgeon du Pyrosome" Compte. rend., Ac. Sci. Paris. T. 94. No. 14, p. 988. 



