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 takes 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 



1 Lumbriculus, Nals,Chaetogaste.r axii Aeolo- gle individual of Myrianida fasciata, which is al- 



soma. lied to Phi/llodoce, produces six young by as many 



ü See John.tton, in the 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. Müller (Naturgesch. the caudal extremity.* 



einiger Wurm-Arteu des süssen und salzigen Was- 5 See the experiments upon this subject with the 



sers. Taf. II. &c.). For that of Nais proboscidea Lumbriciui by Reaumur, Bonnet, Tremhley, and 



and Chaetos;aster diaphanus, see Gruitkuisen, Raesel. Dalyell {Froriep^s neue Not. No. 331, 



Nov. Act. Acad. Nat. Cur. XI. p. 243, Tab. XXXV. 1840, p. 1) has oljserved a simUar mode of repro- 



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



of Aeotosoma, see Orsted in Kröyer^s Naturhist. 6 This has been observed by Grube, with Polia 



TidskrUt. IV. PI. III. fig. 7 ; and for that of iVe- deline.ata (Zur Anat. d. Kiemenwürmer, p. 58); 



rets prolifera, see Müller, Zool. Dan. II. p. 1Ö, 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 Wagner, Prod. Hist, gener. loc. cit. Tab. I. 



ati multiply in the same way. Quatrefages (Fro- fig. 9, 10 (Sanguisuga and ISephelis) ; Stannius, 



riep^s neue Not. No. 726,1845, p. 344)'lias 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. lilt. &c. p. 87, Tat' 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 fVieg- 



with Filograna implexa, a young animal detach- mann\s Arch. 1845, I. Taf. I. fig. 13 (Poli/noe cir- 



iug itself from the caudal end of this Serpula. 1 have rata). If the bodies which H. Meckel has figured 



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



allied to 6'e(/;u/a. According to Milne Edwards 23) as the eggs of /yumft/jcus <erre.s<r(S, are really 



(Ann. d. Sc. Nat. III. 1845, p. 180, PI. XI.) a sin- such, which 1 think is doubtful, they differ much 



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



(Deber die Fortjjflanzung durch Theilung bei Nais mehrung bei Nais proboscidea, in fViegman7i''s 



proboscidea, in tViegmann's Arch. 1850, p. 293). Arch. 1851, p. 134, Taf. II. fig. I.-IIl. ; andA'ro/tn, 



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



tion with this animal, and according to him it is a Syllis prolifera und Autolytus prolifer. Ibid. 1802^ 



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

 tyllis, described by Frey and Leuckart. See fui"- 



