On the Young Stages of a few Annelids. 315 



have further diminished in size as well as number, the convolu- 

 tions of the digestive cavity are more distinct, the antennae 

 have decreased in length, and the vibratile rings have lost 

 their former power. In a subsequent stage (Fig. 11) the head 

 has become more distinct, the anterior vibratile ring scarcely 

 exceeds the diameter of the body, and the antennas are quite 

 prominent. The little worm is only rarely fished up in this 

 stage, swimming about very slowly, and becoming somewhat 

 more active when creeping upon the bottom, where they now 

 prefer to remain. This is their most advanced nomadic stage, 

 and from their subsequent habits it is necessary to keep them 

 in confinement in order to follow their later changes. 



We find in Fig. 11 the pigment spots becoming smaller 

 than in preceding stages ; the convolutions of the digestive 

 cavity, which has acquired a light yellowish coloring, are 

 extremely well defined. Up to this time we have still no trace 

 of feet, bristles, or appendages of any sort, except the two 

 tentacles of the head ; and, were it not for these, it would seem 

 as if the young worm were the larva of some Nemertes-like 

 animal, notwithstanding the different development of Nemer- 

 teans observed by Muller,* Busch,f Gegenbaui'4 Krohn,§ 

 "Wagener,|| Leuckart and Pagenstecher,^f and others, which, 

 when we know more of the general plan of development of 

 Annelids, may after all not present any greater differences 

 when compared to the present type of growth, than we find in 

 the embryology of Echinoderms, between the plutean and 

 sedentary mode of development. There can be no doubt that 

 we have in Annelids as in Echinoderms closely allied genera 

 undergoing a widely different metamorphosis, an additional 



* Muller J., 1. c, in Archiv f. Anat. u. Phys., 1847. 



f Busch W., Entwickelung u. 8. w. 1. c, p. 107. 



% Gegenbaur C, 1. c. ; in Zeitsch f. Wiss. Zool., 1853, V. p. 346. 



§ Krohn A., 1. c. ; in Archiv f. Anat. u. Phys., 1856, p. 78. 



| Wagener R. ; in Archiv f. Anat. u. Phys., 1857, p. 204. 



^[ Leuckart u. Pagenstechek ; in Archiv f. Anat. u. Phys., 1858, p. 569. 



