On the Young Stages of a few Annelids. 319 



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 laving eggs 

 within the tube in which they live, in Terebella, 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 for 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 

 during a night that the smooth sides of the vessel are complete- 

 ly covered with small limestone tubes, formed by the young 

 Spirorbis hatched since the evening before. 



We may perhaps find in our Spirorbis the explanation of the 

 anomalous development of Terebella Medusa* observed by Bate 

 in what he calls uterine sacs, which may prove identical with the 

 tubes containing the eggs and forming strings (Fig. IS) which I 

 have observed in this species, placed on each side of the aliment- 

 ary canal, in the naked part of the body immediately behind the 

 collar. The young are quite advanced within the body of the 

 parent, previous to the transfer of the egg sacs to the cavity of the 

 tube, where they complete the greater part of their growth. Bate 



* Bate C. S. ; Terebella Medusa; in A.nn. and Mag. Nat. Hist., 1851. VIII., 

 p. '237. 

 JUNE, 1866. 24 Ann. Ltc. Nat. Hibt., Vol. VIII. 



