POLYCHAETA. 



469 



In some genera of the Syllidae the process is more complicated.* 

 The Heterosyllid condition is assumed (Fig. 375, /), and the worm 

 divides into an anterior non-sexual portion, and into a posterior 

 sexual portion (Fig. 375, //), which after separation acquires a new 

 head, and becomes an independent male or female worm. The 

 anterior non-sexual portion develops after separation new anal 



FIG. 374. Autolytus 

 cornutus, with the 

 male animal Polybos- 

 trichus (after A. 

 Agassiz). F tentacles; 

 CT tentacular cirri 

 of the asexual worm; 

 / tentacles ; ct tenta- 

 cular cirri of the male 

 Polybostrictms. 



FIG. 375. Diagrams illustrating the asexual 

 reproduction of different Chaetopods. /, 

 the heteronereid or heterosyllid stage ; A 

 non-sexual anterior part ; B posterior sexual 

 part. II, the posterior sexual part is 

 separating from the anterior non-sexual 

 (Syllis hyalina). Ill, the same in Autolytvs, 

 the hinder zooid develops a head before 

 separation. /Fand Fbudding in Autolytus, 

 Myrianida,etc., in which the zone of fission, 

 after producing the head of the sexual worm, 

 persists (Z), and gives rise to a chain of 

 sexual zooids (C, D). Altered from Benham. 



D! 



segments, which eventually acquire generative organs and Hetero- 

 syllid setae, and in their turn separate from the anterior portion to 

 form an independent sexual worm, male or female ; in this case the 

 two sexes are similar. In some cases the sexual form may never 



* Schizogamy is the name given to that method of reproduction in which a 

 sexual worm is produced by fission (fissiparous) or by gemmation (geinmiparous) 

 from a sexless worm ; in other words, schizogamy is synonymous with meta- 

 genesis. 



