388 On Alternate Generation in Annelids, 



ing, is to trace the development of an embryo coming 

 from the egg of one of the female individuals into a parent 

 stock similar to that from which the sexual individual was 

 produced, and which should in its turn produce males or 

 females only by division, and not by sexual reproduction. 



It is this link which I have been able to supply, hay- 

 ing had the good fortune to observe in a species of Aiito- 

 lylus of our coast the development of male and female 

 individuals, differing to a degree almost unknown in the 

 class of Annelids,* from parent stocks different from both 

 of these proliferous individuals. I have also succeeded 

 in tracing from the eggs the growth of the young embryo 

 into a parent stock, identical in every respect with the 

 parent stocks from which the males and females were pro- 

 duced by division. There can no longer be any doubt 

 that we have in the higher Annelids an alternate genera- 

 tion. It seems to me highly probable that further investi- 

 gations will show this to be the case for other genera, such 

 as Psammathe, Heteronereis, Exogone, Cystonereis, and all 

 those Annelids in which we find a specialization of a 

 certain number of rings, as is the case in the sexual indi- 

 viduals of Autolytus. Whether alternate generation will 

 explain the phenomena of unsexual reproduction of Nais, 

 cannot be settled without further investigations ; as the 

 contradictory statements of the different authors leave it 

 very doubtful whether there is anything like a parent 

 stock existing in Naidina.f 



* Oersted (Mag.) had observed in Exogone naidina great differences between the 

 two sexes, but thej' were not as striking as in Autolytus. As this genus is closely- 

 allied to Autolytus we may look for phenomena similar to those observed in that 

 genus. 



Oersted (Mag.), Ueber die Entwickelung der Jungen bei einer Annelide, etc. 

 Wieg. Archiv, 1845, I., p. 20. See also Kolliker on the development of Cystoue- 

 reis, Nouv. M(5m. de la Soc. Helvet. des Sc. Nat. VIII., 1847. 



t Schultze (Dr. Max Sigm.), Ueber die Fortpflanzung durcli Theilung bei Nais 

 proboscidca. Wieg. Archiv, 184!t, I., p. 293. Lcuckart (Dr. H.). Ueber die uiige- 

 schlechtliche Vermchrung bei Nais proboscidca. Wieg. Archiv, 1851, 1., p. l;>4. 



