368 THE NATURAL HISTORY REYIEW. 



appear to us most worthy of narration. O. F. Mliller, in his 

 Zoologia Danica (1788) figured a small Annelid {Nereis 'prolifera) 

 in the act of reproducing itself by division. This mode of repro- 

 duction among the higher Annelids remained for a long time 

 unconfirmed, and many authors, especially Ehrenberg, began to tlirow 

 doubts upon the observation of Miiller. Ehrenberg even went so far 

 as to establish a division among the worms, founded on their mode of 

 reproduction, and placed N. prolifera in that section in which repro- 

 duction by division did not occur. Shortly after this, however, the 

 researches of Quatrefages and Milne Edwards placed Miiller's 

 observations beyond the shadow of a doubt. They observed prolifica- 

 tion in Syllis and Myrianida. Next Sars observed it in Filograna, and 

 at last it became evident that this mode of reproduction was not 

 confined to the Naidina, and that it might be expected to occur in 

 all the other families of Annelids. The peculiar phenomena preced- 

 ing the separation of the sexual individuals, the fact that tbe eggs 

 and spermatozoa, seemed to be developed only in that portion which 

 w^as to form a new individual, at once suggested the idea that there 

 was an alternation of generation in this group. 



O. E. Miiller had observed that the individuals about to separate 

 were alone filled with, ova, and that these ova were less advanced 

 in those sexual individuals which were farther from the posterior 

 extremity. Quatrefages found in a species of Syllis, reproducing 

 itself by division, that the reproduced form was either a male or a 

 female, and that the anterior part never showed the slightest trace of 

 sexual organs. Milne Edwards found in Myrianida, five or six zooids 

 already well developed, those nearer the tail being the most advanced 

 and he observed that the proliferous individuals were alone provided 

 with sexual organs. Sars observed the same phenomena in Filograna 

 implexa, one of the Serpulea ; and Schmidt in a second species of the 

 same genus, F. Schleideni. The observations of the latter plainly 

 showed that a part of the parent stock passes into the sexual individuals 

 when division takes place. Frey and Leuckart repeated the observa- 

 tions of Miiller to a certain extent ; but they endeavoured to show 

 tbat the development of N. prolifera was a case of budding and not of 

 division, and that there was nothing in its development to justify 

 the assertion of an alternate generation. Krohn, however, (1852) 

 was fortunate enough to observe the whole development of the same 

 species, and it became e^ddeut that the remarkable phenomena which 

 he observed could only be explained on the supposition of an alter- 



