1897.] NATURAL SCIENCES OF PHILADELPHIA. 153 



THE ANATOMY AND DEVELOPMENT OF SPIRORBIS BOREALIS. 

 BY MARY A. SCHIVELY, B. S., M. D. 



The following studies upon Spirorbis were made during the months 

 of July and August at Woods Holl, Mass. This chaetopod annelid 

 is found attached to the brown alga Fucus which grows on boulders 

 and the piles of old wharves in the locality referred to. It is best 

 collected at low tide and seems to limit itself to situations where 

 there is a strong current. The food of the annelid worm consists of 

 infusoria and minute forms of algse. 



From observations made during two summers, and upon material 

 collected from eight localities in the region of Vineyard Sound 

 and Buzzard's Bay, it appears that S. borealis has two breeding 

 seasons. One of these extends from the middle of June to the 

 middle of July ; the other extends through the month of August. 

 During the last two weeks of July no eggs were found either in the 

 body cavity or in the shell. Examining egg-chains on July 6th, 

 nothing but well developed embryos were found, while on July 31st, 

 the very earliest stages of segmentation and undeveloped eggs were 

 found in abundance. 



The shape of the body of S. borealis is sub-cylindrical anteriorly, 

 tapering posteriorly ; there are two grooves, a ventral and a dorsal, 

 in the latter is found the egg-chain. The outer segmentation corre- 

 sponds to the inner, the number of metameres and dissepiments 

 varying from 14 to 20. The segments are somewhat narrower on 

 the ventral than on the dorsal side, probably due to the position as- 

 sumed by the annelid in its shell. The external openings of the 

 segmental organs or nephridia are found on the ventral side near 

 the base of each metamere. On the prostomium are placed eight 

 branchise, one of which is modified into an operculum. These 

 branchiae are branching and filiform, each branching portion being 

 furnished with cilia arranged on either side. The branchiae are ar- 

 ranged in a circum-oval manner. In the usual position of the anne- 

 lid in the shell, the branchise and operculum only are protruded. 



The eggs pass out through the operculum ; its end bears a 

 movable translucent plate of lime which protects the animal from 



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