332 On the Young Stages of a few Annelids. 



assumes the appearance of the adult. The number of rings 

 increases rapidly, the dorsal cirri as well as the tentacles 

 lengthen materially, the stomach proper becomes much nar- 

 rower, and towards the anal extremity a distinct intestine 

 (Fig. 42) has been formed. In a stage preceding, Fig. 40, it has 

 many characteristics of the larva figured by Busch, on Plate 

 VIII. Figs. 1-2 of his Beobachtungen. The serrated bristles of 

 these young worms are not lost, as in other Annelids, where 

 the ringed bristles are always temporary, but remain to form 

 in the adult a brush of long bristles on the posterior side of the 

 dorsal cirri, see Fig. 43 ; with the lower bunch of smooth setse 

 we find the row of hook-shaped bristles first noticed in Fig. 41 ; 

 in Fig. 42 we have already from five to six of these bristles at 

 the anterior rings. The upper brush of serrated bristles is 

 found in specimens measuring no less than four inches in 

 length, not raised in confinement, but collected on the beach, 

 where they are found in company with Polydora, but by no 

 means so commonly. Along the middle of each ring, on the 

 dorsal side of the younger stages, Figs. 39, 40, we find a row of 

 short vibratile cilia ; similar rows, less numerous, of larger 

 cilia, occur on the lower side. The anal ring terminates in the 

 adult in a simple opening with slightly corrugated edges, 

 Fig. 45. 



The general mode of development is so similar to that of 

 Leucodora given by Claparede, and of Polydora as figured in 

 the present paper, that only those stages have been introduced 

 which tended to elucidate the comparison with figures, pre- 

 viously published, resembling them. The resemblance be- 

 tween the young larvae certainly warrants the affinity suggested 

 by Claparede, between Nerine, Spio, and Polydora, who 

 places them with the Ariciaa, an does not justify us in asso- 

 ciating the former with other families, as has been done by 

 Quatrefages in his Systematic Table, and thus bringing them 

 in close relationship with groups having a totally different em- 

 bryonic development, such as Phyllodoce and Nereis. The 



