FISSION 



279 



a region or zone of proliferation (Fig. 148, TV). Moreover, in 

 some species not only is the hinder part of the body converted 

 into a sexual zooid, but the zone of proliferation becomes very 

 active, and produces by gemmation a large number of segments, 



je- 



ez 



Fig. 148. Diagrams 

 illustrating the 

 various stages in 

 the asexual forma- 

 tion of a chain of 

 zooids. (Modified 

 from Malaquin.) 



I, Heteronereid 

 or Heterosyllid 

 stage. A, Non-sex- 

 ual ; A', sexual 

 region of the body, 

 with modified 

 parapodia. 



II, Syllis. The A* 

 hinder sexual re- 

 gion, B, is similarly 

 modified, and will 

 separate from the 

 parent zooid, A, 

 and become an 

 independent zooid. 



III, Autolytus. 

 The hinder zooid, B, develops a head by budding before separation. 



IV, Autolytus, etc. A zone of budding (z) makes its appearance in 

 front of the head of B, and by its growth will give rise to a series of 

 new segments in the middle of the body. 



V, Myrianida, Autolytus, etc. From this zone of budding a very 

 large number of segments have been formed, which have, further, be- 

 come grouped so as to form three individuals, C, D, E ; B is the hind- 

 most zooid, which is either formed from the hinder segments of the 

 parent zooid or is produced by budding, like C, D, E. 



y_ 



w 



A = 



C 



which become marked out, by the appearance of heads at intervals, 

 into a number of zooids, in which genital organs will later make 

 their appearance. A chain of as many as sixteen zooids may be 

 formed in Autolytus (Fig. 148, V) the hindermost by conver- 

 sion of the hinder part of the body of the original " stock," the 

 intervening zooids by gemmation. 



One original " stock," or asexual zooid, thus produces several 

 sexual zooids, but these are only of one sex for a given stock. The 

 males differ in several important characters from the females ; so 

 different, indeed, are the two sexes that before their history was 



