176 THE ANNELIDES. ^ 163. 



Spontaneous transverse fissuration occurs particularly with the Abran- 

 chiati,''' but has also been observed with the Nemertini/-' and Branchiati.''^' 



It occurs usually at the middle portion or at the border between the 

 second and third segments of the body. Very often there may be per- 

 ceived at this point, when this process has somewhat advanced, the place 

 where, with the two future individuals, there will be a new fissuration. If 

 the animal has a proboscis, tentacles, or eyes, these organs are developed 

 with the posterior individual before its final separation.'^' 



These animals have no trace of genital organs, while this process of divi- 

 sion lasts. The individuals thus produced, re-divide, and this division 

 continues until a certain time of the year. It then ceases, and genital 

 organs being developed, reproduction taives place by eggs. 



The extreme vulnerability and reproductive power of many Chaetopo- 

 des, give rise to their frequent multiplication by artificial and accidental 

 division. The fragments thus produced are finally developed, and the mu- 

 tilated animal ultimately regains its lost parts. *^* Some have the power of 

 voluntary division from the least handling of their body,"" and these sep- 

 arated parts are probably developed to new individuals. 



§ 163. 



Most of the Annelides reproduce by sexual organs, and the few Lumbri- 

 cini which, as just observed, multiply by fissuration, have probably, like their 

 allied species, genital organs at certain seasons of the year.*^' 



The eggs of the Annelides- present nothing remarkable ; they are always 

 spherical, and have a chorion and thin vitelline membrane containing a 

 finely-granular vitellus with a germinative vesicle and dot.<'-> This 



I Lumbriculus, Nais, Chatto^aster and Aeolo- gle individual of Mt/rianida fasciata, whicli is al- 



toma. lied to Pliy/lodoce, produces six young by as many 



n See Johnston, in tlie Mag. of Zool. and Bot. I. successively disposed divisions. According to Frey 



1837, p. 534. and Leuckart (Beitr. &c. p. 94, Taf. II. fig. 1), 



3 With the Nereideae. there are with Syllis prolifera also, several young 



4 Fissuration with many species of Nais, has developed simultaneously, one after the other, at 

 already been noticed by O. F. Mailer (Naturgesch. the caudal extremity.* 



einiger Wurra-Arten des sussen und salzigen Was- ■'> See the experiments upon this subject with the 



sera. Taf. II. &c.). For that of Nais proboscidea Lumbricini by Riaiimur, Bonnet, Trembley, and 



and Cfiaetoi^aster diaphanus, see Gruitliuisen, Roesel. Dalyell (Froriep\'i neue Not. No. 331, 



Nov. Act. Acad. Nat. Cur. XI. p. 243, Tal>. XXXV. 1840, p. 1) has observed a similar mode of repro- 



fig. 1, 3 ; XIV. p. 412, Tab. XXV. fig. 2. For that duction with Sabella. 



of Aeolosoma, see Orsted in Kruyer''s Naturhist. 6 This has been observed by Grube, with Polia 



Tidskrift. IV. PI. III. fig. 7 ; and for that of Ne- delineata (Zur Anat. d. Kiemenwurmer, p. 58). 



reis prolifera, see Muller, Zool. Dan. II. p. 16, Meckelia annulata has also the same property. 



Tab. LII. fig. 6. This last species is a very young 1 Aeolosoma. 



Nereis. It is probable that many other Branchi- 2 See iVas:ner, Prod. Hist, gener. loc. cit. Tab. I. 



ati multiply in the same way. Qiiatrefages (Fro- fig. 9, 10 (Sanguisuga and Nephelis) ; Stayiniits, 



riep's neue Not. No. 726, 1845, p. 344)"has recently in Muller's Arch. 1840, Taf. II. fig. 1, 2 {Areni- 



recognised a. Syllis in Nereis prolifera. cola piscatorum) ; Milne Edwards, Ann. d. Sc. 



Sars (Faun. litt. &c. p. 87, Taf. X. fig. 18, 19) Nat. Ill, 1845, PI. V. fig. 2, 3, PI. IX. fig. 43, 44 



has observed multiplication by transverse division (Terebella and Protula); and Sars, in Wieg- 



with Filograna implexa, a young animal detach- mannas Arch. 1845, 1. Taf. I. fig. 13 {Polynoe cir- 



ing itself from the caudal end of this 5er;;u/a. I have rata). If the bodies which H. Meckel has figured 



observed a like division with a Protula, a genus (Muller's Arch. 1844, p. 481, Taf. XIII, fig. 13- 



allied to Serpula. According to Milne Edwards 2^3) as the eggs of Lumbricus terrestris, are really 



(Ann. d. Sc. Nat. III. 1845, p. 180, PI. XI.) a sin- such, which I think is doubtful, they differ much 



* [ § 162, note 4.] See in this connection, Sckitltze ther Leuckart, Ueber die ungeschlechtlichte Ver- 



(Ueber die Fortiiflanzung durch Theilung bei Nais mehrung bei Nais jiroboscidca, in }Viegmann''s 



proboscidea, in IViegmann's Arch. 1850, p. 293). Arcli. 1851, p. 134, Taf. II. fig. I.-III. ; and Krolm, 



He has carefully described this form of multiplica- Ueber die Erscheinungen bei der Fortpflanzung von 



tion with this animal, and according to him it is a Syllis prolifera und Autolytus prolifer. Ibid. 1852, 



true fissuration, and not a gemmation, as that of p. 66. — Ed. 

 Syllis, described by Frey and Leuckart. See fur- 



