THE DEVELOPMENT OF CLEPSINE. 569 



It may be suspected that the other cases of supposed en- 

 togastric proliferation will prove to be susceptible of a similar 

 explanation. 



Although, as I have endeavored to show, the Ctenophora 

 are readily reducible to the general plan of the Actinozoa, yet, 

 considering their many peculiar characters, I think it is ad- 

 visable to separate them from the Coralliyena, as a distinct 

 natural order. 



Moreover, the JPhysemaria must undoubtedly be placed 

 in this section, which will, therefore, consist of the following 

 natural orders: Physemaria, JPorifera, Hydrozoa, Coralli- 

 gena, Ctenophora. 



Section III. — I concur in the proposal of Biitschli 1 to es- 

 tablish a group, JVematorhyndia, for the genera Chcetonotus, 

 PJehinoderes, and their allies, to which reference is made at p. 

 101. The Nematorhyncha are divisible into the Gastrotricha a 

 (Chcetonotus, Chcetura, Cephalidium, Ichthydium, Turbanel- 

 la, JTemidasys, and Dasydites), which are ciliated on the 

 ventral surface of the body, and the Atricha (Echinoderes), 

 which possess no cilia. Biitschli finds two convoluted water- 

 vessels analogous to those of the Motifera, but apparently 

 not ciliated, in Choetonotus. 



Section IV. — Our knowledge of the development of the 

 IFtrudinea has received an important addition in the " Me- 

 moire sur le developpement embryogenique des Hirudinees," 

 by M. C. Robin ; who, among other important contributions 

 to embryology, has rectified some important errors of Rathke 

 respecting the early stages of the development of Clepsine. 

 I have found the description and figures of the various stages 

 of cleavage, and of the steps by which the blastoderm is con- 

 verted into the young Clepsine, given in this memoir, to be 

 exceedingly accurate. 



The whole process in Clepsine is very similar to that which 

 has been described in Euaxes by Kowalewsky, 3 and shares 

 with it the remarkable peculiarity that the first-formed por- 

 tion of the blastoderm becomes the hfemal region of the body. 



1 ''Untersuchungeniiber freilebende Nematoden und die Gattung Chaztono- 

 tus." {Zeitschrift fur wiss. Zooloqie, 1876.) 



2 See H. Ludwig, " Ueber die Ordnung Gastrotricha." (Zeitsclirift fur wiss. 

 Zoologie, 1876.) 



3 " Embryologische Studien an Wurmern und Arthropoden." (" Mern. de 

 l'Acad. Imp. de St.-Petersbourg," 1871.) 



