THE DEVELOPMENT OF CLEPSINE. 569 



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

 togastiic proliferation will prove to be susceptible of a similar 

 explanation. 



Although, as I have endeavored to show, the Ctenopliora 

 are readily reducible to the general plan of the Actinozoa^ 3'et, 

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

 visable to separate them from the (Joralllgena^ as a distinct 

 natural order. 



Moreover, the Physemaria must undoubtedly be placed 

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

 natural orders : Fhysernaria^ Porifera, Ilydrozoa, Coralli- 

 gena, Ctenophorcu 



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

 tablish a group, Neniatorhyncha^ for the genera Chatonotifs, 

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

 101. The Nematorhyvicha are divisible into the GastrotricJia ^ 

 ( Chmto7iotus^ Chmtura, CephaUdium^ Ichthydlum, Turhcmel- 

 la., Hemidasys, and Jbasydites), 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 Chcetonotus. 



Section IV. — Our knowledge of the development of the 

 Ulrudinea has received an important addition in the " Me- 

 moire sur le d^veloppement 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,^ and shares 

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

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



* " Unterauchunsfen libcr freilebende Neraatoden und die Gattung Ch(X.tono- 

 tusy {ZeiUchriftfi'ir wise. Zonlogie^ 187fi. ) 



2 See H. Ludwig, " Ueber die Ordaung Gastrotricba." {Zeitsclirift fur wiss. 

 Zoologie, 1876.) 



3 " Embrvolosriscbe Studien an Wurmern und Arthropoden." (" Mdm. de 

 I'Acad. Imp." de St.-Pctersbourg," 1871.) 



