$ 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 Lovén in Wiegmann’s Arch. 1842, I. p. 
302, Taf. VIL. (Nereis); Sars, Thid. 1845, I. p. 
12, Taf I. fig. 1-21 (Polynoz); Orsted, Ibid. 
p. 20. Taf. II. peToe one) ; and Milne Edwards, 
Ann. da. Sc. Nat. Ill. 1845, p. 145, Pl. V.-IX., 
or, Froriep’s neue Not. No. 721, p. 257 (Tere- 
bella, Protula, and Nereis). Kaélliker (in MS. 
already cited) has also observed the development of 
an Exzogone, and of a Cystonerets, 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 irregular 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, 
repr ing the devel of Protula, from 
which it would appear that other Branchiati also are 
developed like the Hirudinei; see Ann. d. Sc. Nat. 
loc. cit. Pl. IX. fig. 47.* 
8 One ought therefore to be careful about form- 
ing distinct genera from these larval Branchiati. 
Thus, Sabellina brachycera, described by Du- 
sardin (Ann, a. 8c. Nat. XI. 1839, p. 291, Pl. VIL. 
* [§ 169, note 2.) or the embryology of Poly- 
noé, see Desor, loc. cit. p.12. It agrees closely 
with that of Nemertes ; see also Max Miiller, in 
Miller's Arch. 1851, p. 323. — Ep. 
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. Pl. VII. fig. 24, 25). Anisomelus 
luteus, of Templeton (Transact. Zool. Soc. II. 
1841, p. 27, Pl. 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 Lumbrinereis of De Blainville. 
The new animal described by Muller and Busch 
(Miiller’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.+ 
+ [§ 169, note 3.] See Quatrefages (Sur ’Em- 
bryogenie des Annélides, in Aun. d. Sc. Nat. X- 
1848, p. 163). - Ep. 
