and the Embryology of Autolytus cornutus. 387 



his class of Somatotoma. These observations of Sars 

 were soon after repeated in a second species of the same 

 genus, Filograna Schleideni, by Schmidt; and his observa- 

 tions plainly show that a part of the parent stock passes 

 into the sexual individuals when the division takes place. 

 Only one individual is formed at a time in this species. 

 Frey and Leuckart * repeated the observations of Miiller in 

 ^^ Nereis prolifera''^ to a certain extent: they found seve- 

 ral of the young in a slightly advanced state of develop- 

 ment ; but as their observations were intended to show that 

 the development of Nereis prolifera was a case of budding 

 and not one of division, that there was nothing in the 

 development to justify the assertion of an alternate gene- 

 ration made by Quatrefages, and as their conclusions 

 were based upon these slightly developed males and fe- 

 males, it is not astonishing that we find them assert that 

 there is not the slightest difference between the young 

 and the parent stock, and that they never found sperma- 

 tozoa developed in the former. It was not until Krohnf 

 was fortunate enough to observe the whole development 

 of Nereis [Autolytus) prolifera, that it became evident 

 that the remarkable phenomena which he observed con- 

 nected with the differences developed in the male and 

 female young could only be explained on the supposition 

 of an alternate generation. He dwells particularly on the 

 striking difference between the males and females, and is 

 led to believe that Miiller % must have observed the male of 

 his Nereis prolifera, and described it as a different spe- 

 cies, (Nereis corniculata,) on account of the great differences 

 of the anterior part. He says, the only link now want- 



* Frey (Dr. H.) und Leuckart (Dr. R.) Beitriige zur Kenntniss Wirbelloser 

 Thiere, mit besoiiderer Beriicksiclitiguiig der Fauna des Norddeutsclien Meeres. 

 Braunschweig, 1847. 



t Krohn (Dr. A.) Ueber die Erscheinungen bei der Fortpflanzung von Syllis 

 prolifera und Autolytus prolifer. Wiegmau. Archiv 1852, 1., ]). 66, I'l. III., fig. 1. 



t Zool. Dan., Tl. 52, tig. 1-1, p. 15. 



