of a few Annelids. 215 



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 ^; but, judging from the differences existing 

 between specimens of our coast and the descriptions of Pagen- 

 stecher, it certainly is not the S, spirillum of Lamarck investi- 

 gated by him : the shape of the bristles of the three large 

 clusters on the collar is totally different, as well as the arrange- 

 ment of the small rods of the collar, which in our species form 

 a single well-defined loop, placed immediately behind the pos- 

 terior 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 differently; 

 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 J Lam. The eggs, of a dark reddish brown 

 colour, 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 of 

 bristles (as in fig. 25), or else when the strings have been laid 

 they are found on the sides of the body, between it and the lime- 

 stone tube, and here the young undergo their transformations. 

 This is contrary to the statements of Pagenstecher, who says the 

 young undergo their development in the funnel-shaped tentacle, 

 used thus as a sort of breeding- case ; it is, however, more in 

 accordance with what we know of the method of laying eggs, 

 within the tube in which they live, in Terebelloj Serpula, and 

 Protula. 



As is already known from the observations of Milne-Edwards 

 on Protula, the young lead a nomadic life but a short time, 

 and soon build a tube in which they live and complete their 

 growth. Pagenstecher has observed the same thing in Spiror- 

 bis ; and it would appear from my own observations that the 

 nomadic life of Spirorbis is not longer than eight or ten hours. 

 The young Spirorbis has attained quite an advanced stage of 

 growth when it leaves the tube of the parent and swims freely 

 about (in search of a place of attachment) during a night at the 

 outside ; even with specimens kept in confinement, in perfectly 

 clean glass vessels, the young escaping from the egg-cases are 

 rarely caught while swimming about; it frequently happens 



* Report on the Invertebrates of Massachusetts, 1841, p. 8, 



