IN THE ANIMAL KINGDOM. 101 



Otto Mliller in Nais pf^oboscidea, and by Gruithuisen in a 

 species of Nereis. More recently M. Quatrefages lias made 

 similar observations on the Si/llis jjroU/era. This species 

 forms ordinarily but a single zooid at a time, but Mr. 

 Milne Edwards in another annelidan — Myrianida fasciata 

 — has seen as many as six in process of formation at the 

 same time from the terminal segments of the parent. The 

 first formed and most complete was situated furthest back, 

 and each newer zooid presented a less developed structure 

 than the preceding one. The anterior or youngest ha<l 

 only ten rings, the second had fourteen, the third sixteeTi, 

 the fourth eighteen, the fifth twenty -three, and the last or 

 caudal one thirty rings. In some of the species named, the 

 fissiparous multiplication has very markedly the character 

 of a process ancillary to sexual reproduction, for the zooid.s 

 when thrown off speedily develope the appropriate organs, 

 but retain life only long enough to impregnate or mature 

 the resulting broods of ova.* In other cases, perhaps, 

 multiplication may go on indefinitely, by the detached 

 zooids repeating the same fissiparous process — the forma- 

 tion of sexual organs appearing to depend in some degree 

 on external circumstances. Midtiplication may also be 

 effected by artificial division, in some cases in which the 

 fissiparous process does not seem to come into play as a 

 spontaneous mode of increase. *[* 



In the sexual relations of the Annelida there is consider- 

 able variety, hemaphroditism beinj^ a common character 

 among the Terricolse and Suctoria, while the sexes are 

 generally separate in the other orders. There is no evi- 

 dence of self-impregnation in any. 



* Quatrefages Ann. Des. Sci. Nat. (1814) T. I., p. 22. Edwards, Oi:.. 

 Cit. (18i5),T. III., p. 170. Dr. A. Thomson, Cyclop. Anat. and Physiol., 

 Art. Ovum., p. 32-33. 



t Siebold, Compar. Anat. I., § 163. 



