182 THE ANNELIDES. ^ 169. 



tween the feet of many Brancliiati, serve for the escape of the sperm and 

 eggs.'''' With others, the cavity of the body opens outwardly, probably by 

 a loss of the last segment, especially with those which are viviparous. '''* 



The water is undoubtedly the medium of fecundation, and i-eceives the 

 sperm from the males, probably through orifices like those which serve for 

 the escape of eggs with the female. 



With the viviparous Branchiati, water filled with sperm can enter the 

 body and fecundate the eggs through these same openings. 



§ 169. 



The development of the Annelides as far as yet known, occurs after twa^ 

 different types ; but it always commences with a complete segmentation of 

 the vitellus. 



I. With the Hirudinei, after the vitellus has divided into many large- 

 cells, a central one becomes distinguished from the others by its still further 

 division ; this becomes the digestive tube. The others, still dividing, form 

 a primitive embryonic part in which appears the future ventral and nervous 

 portion. 



The embryo is at first spherical, and ultimately is covered with a delicate' 

 ciliary epithelium. A kind of sucker is then developed upon a certain 

 point of its surface ; this connects with the stomach, and through it is re- 

 ceived, for food, the albumen surrounding the embryo. It then gradually 

 lengthens, and, losing its ciliary epithelium before the escape from the egg, 

 a sucker appears upon the posterior extremity, and it finally becomes- 

 fully developed without a Metamorphosis.'^' 



II. With the Branchiati, there is a complete metamorphosis. The seg- 

 mentation of the vitellus is uniform throughout, and this last is finally 

 changed into a round embryo — which, escaping from the egg, swims freely 

 about like an Infusorium, by means of the ciliated epithelium which covers 

 its whole body. The embryo then lengthens, and the epithelium disappears 



4 According to Milne Ediüards' observations nelidea has recenUy appeared in the Neue Schweiz, 



upon several Capitibranchiati, as Terebella, Ser- Denkschr. VIII.* 



pula, Protula, &c., the eggs are glued together in 5 According to my friend H. Koch of Trieste (in 

 masses by au albuminous substance, and attached the MS. just indicated), the eggs of a species allied 

 to the stones of the anterior border of their cases ; to Eunice sanguinea, are developed in the cavity 

 Bee Ann. d. So. Nat. III. 1845, p. 148, 161, Fl. V. of the female body, whence the young escape 

 fig. 1, PI. VII. fig. 28, PI. IX. fig. 42. With Poly- through a rupture of its posterior e.xtremity. 

 noc cirrata, on the other hand, masses of eggs are 1 See F. de Filippi, Lettera sopra I'Anatomia, e 

 attached and borne al)out on the scales of their lo sviluppo delle Clepsine, Pavia, 1839, Tav. II. ; 

 body ; see Sars, in fViegmann''s Arch. 1845, I. p. Grube, Untersuch, über die Entwick. d. Clepsine, 

 13, Taf. I. fig. 12. With the females of Exogone p. 15, Taf. I., and Frey, Zur Entwickel. von. Nephe- 

 and Cystonereia, the eggs ai-e situated in longi- lis vulgaris, in Froriep\'i neue Not. No. 807, 

 tudinal rows upon the ventral surface ; see Örs^erf, 1846, p. 228. The old observations of £. /f. Jfe- 

 in tViegmann's Arch. 1845, I. p. 21, Taf. II. fig. ber {Meckel's Arch. 1828, p. 366, Taf. X. XI.) 

 4, and Külliker, in an as yet unpublished memoir and R. H^asner (Isis, 1832, p. 398, Taf. IV.) agree 

 for the Helvetic Society, titled -. Einige Worte zur very well with those of Filippi 

 Entwickelungsgeschichte von Eunice, von H. Koch As yet, we possess nothing upon the develop- 

 in Trieste, mit einem Nachwort von Kölliker. ment of Lumbricini, whose young, as is known, like 



[Additional note.] The often-quoted memoir of those of the Hirudinei, leave their cocoons without 



Koch and Külliker on the development of the Au- undergoing any metamorphosis.f 



* [^ 108, note 4.] According to Felix Dujar- servation, from its singularity, requires confirm- 



din (Ann. d. Sc. Nat. XV. 1851, p. 298) Exogone ation. — Ed. 



pusilla is androgynous. Beside the well-known 1 [ § Iß^i ""te 1] For the embryology of iVe- 



pediculated ovarian sacs on the ventral surface, mertes, see Desor, Boston Jour. Nat. Ilist. VI. p. 



each segment of the body, e.xcept the first two, , 1. The general facts accord with those meutioued. 



has, with this species, a dorsal, fusiform cirrus, in in the text. — Ed. 

 which are developed spermatic particles. This ob- 



