THE DEVELOPMEXT 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 Acti?iozoa., yet, 

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

 visable to separate them from the CoralUgena^ as a distinct 

 natural order. 



Moreover, the Physemaria must undoubtedly be placed 

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

 natural orders : Fhysemaria, Porifera, Ilydrozoa., Coralli- 

 gena^ Ctenophora, 



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

 tablish a group, Kematorhynclia^ for the genera Chatonotus^ 

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

 101. The Kernatorhyncha are divisible into the Gastrotricha ^ 

 (Chc^tonotiis, Chcetura^ Cephalklium^ Ichthydhnn^ Turhanel- 

 la, Semidasys, and Pasydites), 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 Potifera, but apparently 

 not ciliated, in Choetonotus. 



Sectiox IY. — Our knowledge of the development of the 

 Ulrudinea has received an important addition in the " Me- 

 m.oire sur le developpement embryogenique des Hirudinees," 

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

 to embryology, has rectified some important errors of Rathke 

 resj^ecting 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 wdiich 

 has been described in Euaxes by Kowalewsky,^ and shares 

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

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



1 " Untersiicliuno^en fiber frellebende Neraatoden und die Gattung Ckaitono- 

 tus.'''' {Zeitschrift^fiir wiss. Zoolo(fie^\%'l'o,) 



2 See H. Ludwig, " Ueber die Orduung Gastrotriclia." {Zeitschrift fur wiss. 

 Zoologw, 1876.) 



3 " Embrvolooriscbe Studien an Wurmem und Arthropoden." (" Mem. do 

 1' Acad. Imp." de St.-Fetersbourg," 1871.) 



