134 LILIAN SHELDON. 



Seeliger 1 observed the pit in the embryo Clavellina, though 

 he found no connection between it and the nervous system. 



Salensky 2 describes the ciliated pit in the embryo of Sal pa 

 democratica as a short tube forming a communication 

 between the pharynx and the anterior end of the nervous 

 system, which is at first hollow, but afterwards becomes solid. 



Kupffer 3 found no communication between the mouth and 

 nervous system in the embryo ofAscidia mentula. 



Van Beneden and Julin 4 describe the ciliated pit in the 

 embryo of Clavellina rosaceus, and also state that on its 

 ventral side it communicates" with a mass of tissue lying 

 ventral to it which gives rise to the gland. From their figures 

 I believe this mass of tissue to be homologous with what I 

 have described above as the posterior ventral part of the 

 nervous system in Amarsecium. In the latter I assume that 

 this structure is a part of the nervous system on account of 

 its histological features, and also from the fact that it connects 

 the dorsal part of the nervous system with the nerve-cord of 

 the tail. 



Comparison of Condition tn Embryo Amar^cium with 

 the Various Types in Adult Ascidians. 



I have not worked out the development from the oldest 

 unhatched embryo into the adult form owing to lack of 

 material, so that the views here put forward must be merely 

 provisional. 



There can be little doubt that the part of the embryonic 

 nervous system, which is found persisting in the adult, is the 



1 Seeliger, O., loc. cit. 



2 Salensky, W., " Ueber die Embryonale Entwicklungsgeschichte der Sal- 

 pen," ' Zeit. flir wissen. Zool.,' 1876. 



3 Kupffer, C, "Die Entwicklung der Einfacken Ascidien," 'Arch, fur 

 Mik. Anat.,' 1872. 



4 Ed. van Beneden et Ck. Julin, " Le systeme nerveux central des Ascidies 

 et ses rapports aveo celui des larves urodeles," ' Arck. de Biologic,' tome v, 

 1884. 



