^169. 



THE ANNELIDES. 



183 



except upon the belt-like parts of the two extremities. The future ante- 

 rior extremity is directed in front during the motions of the animal, and 

 eyes appear upon it; while the other extremity is gradually divided into 

 segments upon which bristles and feet appear.*-' 



While the embryos are thus acquiring the adult form, there appear upon 

 the cephalic extremity and upon the sides of the body, tentacles, cirri, and 

 branchiae, of forms which vary according to families, genera and species. 

 The development of the digestive and circulatory organs occurs also with 

 equal pace.*^^ 



2 See LovM in Wie srmann'' s Arch. 1842, I. p. 

 302, Taf. VU. {Nereis); Sars, Ibid. 1845, I. p. 

 12, Taf I. fig. 1-21 (Polynoe); Örsted, Ibid, 

 p. 20. Taf. II. (Exog-one) ; and Milne Edwards, 

 Ann. d. So. Nat. III. 1845, p. 145, PI. V.-IX., 

 or, Froriep^s neue Not. No. 721, p. 257 {Tere- 

 bella, Protula, and Nereis). Kolliker (in MS. 

 already cited) has also observed the development of 

 an Exogone, and of a Cystonereis, an allied ge- 

 nus. Here the embryo is not formed through a 

 complete and uniform segmentation of the vitellus, 

 but, as with the Hirudinei, the formation is preced- 

 ed by an u-regular division of that portion to be the 

 ventral and nervous parts. He, at the same time, 

 calls the attention to a figure of Milne Edwards, 

 representing the development of Protula, from 

 which it would appear that other Branchiati also are 

 developed like the Hirudinei ; see Ann. d. Sc. Nat. 

 loc. cit. PI. IX. fig. 47.* 



3 One ought therefore to be careful about form- 

 ing distinct genera from these larval Branchiati. 

 Thus, Sabellina brachycera, described by Du- 

 -ardin (Ann. d. Sc. Nat. XI. 1839, p. 291, PI. VII. 



* [ § 169, note 2.] Tor the embryology of Poly- 

 noe, see Desor, loc. cit. p. 12. It agrees closely 

 with that of Nemertes ; see also Max Müller, in 

 Mailer's Arch. 1851, p. 323. — Ed. 



fig. 6), is only a larval Terebella, as will be seen 

 by referring to Milne Edwards'' figures of the de- 

 velopment of Terebella nebulosa (Ann. d. Sc. 

 Nat. loc. cit. PI. VII. fig. 24, 25). Anisomelus 

 luteus, of Templeton (Transact. Zool. Sue. II, 

 1841, p. 27, PI. XV. fig. 9-14), is perhaps only a 

 young Serpula. 



The absence of branchiae and blood-vessels 

 which Quatrefages has noticed with many small 

 Branchiati of which he has made new genera 

 (as Aphlebine, and Doyeria, &c.), would lead one 

 to suspect that they are only larvae ; see Ann. d. 

 Sc. Nat. I. 1844, p. 18, or Froriep's neue Not. No. 

 726, p. 341. H, Koch (see above, § 168, note 5) 

 has lately observed that the young individuals 

 found in the body of Eunice are identical with 

 the Lmnbrinereis of De Blainville. 



The new animal described by Müller and Busch 

 (Mailer's Arch. 1846, p. 104, Taf. V. fig. 3-5, and 

 1847, p. 187, Taf. VIII. fig. 1-3) under the name 

 of Mesotrocha sexoculata, appears likewise to 

 be only a young larva of an Annelid.t 



f [ § 169, note 3.] See Quatrefages (Sur I'Em- 

 bryogenie des Ann61ides, in Aim. d. Sc. N^t. X- 

 1848, p. 163). - Ed. 



