242 Mr. A. Agassiz on the Young Stages 



Fig. 7. Spicula of C. celata. 



Fig. 8. A few of the cells of Orbitoides Fosteri, from Dr. Carpenter's 



figure, after Ehrenberg : a, cell next primordial cell ; b, b, stolons 



or stems imiting the cells. 

 Fig. 9. A portion of an undescribed Cliona immersed in the shell of Pecten 



Magellanicus : a, a, lobes of the sponge corresponding to the 



cells in fig. 8 ; b,b, stolons or stems. 



. Plate VIII. 



Fig. 1. Spicula of Cliona Mazatlanensis : a, pin-like spicula j b, fusiform 



ditto ; c, c, minute or third form of ditto. 

 Fig. 2. Spicula of C. vermifera : a, pin-like spicula ; b, b, the second or 



worm-like ditto. 

 Fig. 3. Ditto of C. globulifera. 

 Fig. 4. Ditto of C. Carpenteri : a, a, pin-like spicula; b, fusiform ditto; 



c, c, the third or minute form of ditto. 



XXXVII. — On the Young Stages of a few Annelids. 

 By Alexander Agassiz. 



[Concluded from p. 218.] 



Polydora, Bosc {Leiicodora, Johnst.). 



Claparede having given, in his ' Beobachtungen/ a very com- 

 plete history of the development of what he calls Leucudora 

 ciliata, the following observations would be superfluous as far as 

 they relate to new phases in Poly dor a, but may be useful in 

 clearing up the confusion existing concerning the identity of 

 Leucodora, Johnst._, and Folydora, Bosc. Quatrefages, in his 

 Synoptic Table ^, has introduced these two genera as distinct, 

 and separates them on account of the remarkable structure of 

 the bristles of the fifth ring in Polydora, which he says is not 

 to be found in Leucodora : this must evidently be a mistake, as 

 Johnston^s figure t certainly possesses the peculiar bristles of 

 the fifth ring, as maintained by Claparede in his *Beobach- 

 tungen.' Yet, notwithstanding this correction of Quatrefages 

 by Claparede J, in his review of the system proposed by the 

 former, and the accurate description given by him (Claparede), 

 in Miiller's 'Archiv^§, o^ Polydora cornutaj we find him asso- 

 ciating with the genus Polydora, in his embryology of Leucodora 

 ciliata f a genus which is certainly not Polydora as he himself 

 has limited it, but may be a species of Spio or Nerine, or per- 



* " Note sur la Classification des Annehdes," in Comptes Rendus, 27 

 March, 1865 (Annals, ser. 3. vol. xvii. pp. 1, 107). 



t " Miscellanea Zoologica," in Mag. Zool. Bot. 1838, ii. p. 66. 



X Bibliotheque universelle de Geneve, Avril 1865. [Annals, ser. 3. 

 vol. xvii. p. 100.] 



§ " Ueber Polydora cornuta, Bosc," in Archiv fur Anat. u. Phys. 1861 

 p. 542. 



