318 On the Young Stages of a few Annelids. 



anal ring, in accordance with the observations of all writers on 

 the subject. 



Spurokbis Spirillum, Gould (non Pagenst. ; an Lam. f)\ 



The history of the development of Spirorbis has been given 

 in full by Pagenstecher ;* I bring up the subject here to show 

 some differences in our observations, quite important as far as 

 they bear upon the mode of development of the tentacles, and 

 refer to a few features respecting the peculiar tendency of the 

 development in these Annelids which has not been sufficiently 

 dwelt upon. 



The species to which my observations are limited is found 

 attached mainly upon Fucus ; it is undoubtedly the Spirorbis 

 spirillum of Gould,f but judging from the differences existing 

 between specimens of our coast, and the descriptions of 

 Pagenstecher, it certainly is not the S. spirillum of Lamark 

 investigated by him; the shape of the bristles of the three 

 large clusters on the collar is totally different, as well as the 

 arrangement of the small rods of the collar, which in our 

 species form a single well defined loop, placed immediately 

 behind the posterior bundle of long bristles, entirely unlike the 

 arrangement of the same parts as described by Pagenstecher. 



The development of the eggs also takes place quite different- 

 ly, and the present species, although furnished with a large, 

 simple, funnel-shaped tentacle, serving as an operculum, does 

 not use it as an ovarian case, as has been observed by 

 Pagenstecher in S. spirillum Lam. The eggs, of a dark reddish 

 brown color, are found in strings formed of two rows (Fig. 18) 

 either on each side of the alimentary canal in the anterior part 

 of the body, where in the adult we find a considerable space free 



* Pagenstecher H. A. ; Untersuchungen ueber niedere Seethiere aus Cette. Ent- 

 wickelungsgeschichte u. Brutpflege v. Spirorbis spirillum; in Zeits. f. Wiss. 

 Zool., 1863, XII., p. 487, PI. 38, 39. 



\ Gould A. A. ; Report on the Invertebrates of Massachusetts, 1841, p. 8. 



