On the Young Stages of a few Annelids. 325 



jBosc, but to some closely allied genus, as suggested above. It 

 is not probable that such an accurate observer as Claparede 

 would have overlooked this segment, so prominent in the young- 

 est specimens of our Polydora, as well as the presence of the 

 glands, so early developed in the young worm, and which he 

 noticed in his description of the adult in Miiller's Archiv. In 

 my earlier observations I made a similar mistake between young 

 of Polydora and Nerine, and it was not till the striking differ- 

 ence of the fifth ring and the presence of glands was noticed, 

 that I could afterwards always readily distinguish the young of 

 these two genera, so easily mistaken at first sight. 



I shall introduce a few of the stages of Nerine, with a short 

 description of the adult, for the sake of comparing them with 

 the different stages of Polydora, which will be given more in 

 detail, and of identifying them, as far as possible, with those 

 observed by Claparede. It is apparent at first glance, on 

 comparing his drawings of Leucodora with those here given 

 of Nerine and Polydora, that they represent closely allied 

 genera ; but as similar young stages of other genera have 

 also been figured by Leuckart and Pagenstecher as Spio, as 

 well as by Busch and by Frey and Leuckart,* the adults of 

 which are not known, we must be exceedingly careful in our 

 identifications of apparently closely related forms, and give 

 these identifications more as hints for future observers, than as 

 positive statements. 



The young of Polydora and Nerine, like the young of Leu- 

 codora Claparede, are kept in confinement with the greatest 

 ease; hence the possibility of tracing the changes of growth in 

 a connected manner until they have assumed unmistakably the 

 features and habits of the adult, and built their cases on the 

 bottom of the jars where they are confined. The youngest 

 stages observed, Fig. 26, are considerably more advanced than 

 those of Claparede, having already lost, if they ever pos- 



* Frey H. u. Leuckart R. Beitrage zur Kenntniss wirbelloser Thiere. 

 Braunschweig, 1847. PI. 1, Fig. 19, p. 98. 



