182 THE ANNELIDES. § 169. 



tween the feet of many Branchiati, 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 receives the 

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

 the escape of eggs with the fenrale. 



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 two 

 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 embi'yo 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 jEdM;ar(/s' observations nelidea has recently appeared in the Neue Schweiz. 



upon several Capitibranchiati, as Terebella, Scr- DenUschr. VIII.* 



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

 masses by an 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 san^uinea, are developed in the cavity 

 see Ann. d. Sc. Nat. III. 1845, p. 148, 101, I'l. V. of the female body, whence the young escape 

 fig. 1, PI. VII. fig. 28, PI. IX. fig. 42. With Poll/- through a rupture of its posterior extremity. 

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

 attached and borne about on the scales of their lo sviluppo delle Clepsine, Pavia, 183S), Tav. II. ; 

 body ; see Sars, In fViegmannKi Arch. 1845, I. p. Grube, Ilntersuch. iiber 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 Cj/s^onereis, the eggs are situated in longi- lis vulgaris, in Froriep''s neue Not. No. 807, 

 tudinal rows upon the ventral surface ; seeOrsted, 1846, p. 228. The old observations of JE. /f. fr?- 

 in Wiegmann's Arch. 1845, I. p. 21, Taf. II. fig. ber {Meckel's Arch. 1828, p. 366, Taf. X. Xl.y 

 4, and Kolliker, in an as yet unpublished memoir and R. (Vasner (Isis, 1832, p. 398, Taf. IV.) agree 

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

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

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



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



Koch and Kdlliker on the development of the An- undergoing any metamorphosis.f 



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



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



pusilla is androgynous. Beside the well-known t [§ 169, note 1] For the embryology of Ne- 



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



each segment of the body, except the first two, 1. The general facts accord with those mentioned 



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

 which are developed spermatic particles. This ob- 



