Glass 1. Chcetopoda. 



171 



parapodia. Sometimes eyes and auditory organs, wliicli do not 

 occur in the adult, are present. 



Fi". 134. 



Fig. 135. 



Fig. 134. Diagram of the reproductive apparatus of an Earth-worm ; the animal is 

 dissected from the mid-dorsal line and spread out. 8 — 14, 8th to 14th bristle-hearing seg- 

 ments. ovary, od oviduct, sb vesicula seminalis, sg spermatheca, t testis, vd vas deferens, 

 vd' its outer end, ce receptaculum ovorum. The transverse hnes represent the septa. — Orig.- 



Fig. 135. Larva of Nereis, a anus, m mouth, o eye. — After Gotte. 



Asexual reproduction occurs in not a few members of 

 both groups. In some cases tbere is a simple transverse fission; 

 the animal divides into two nearly equal parts, the posterior of which 

 forms a new mouth, prostomium, etc., before the separation; whilst the 

 anterior produces a new hind end. In other cases budding- 

 takes place ; the hindmost segment (or a number of posterior- 

 segments) elongates and develops into a new individual, which then 

 separates from the parent. Sometimes before separation, the latter 

 begins to produce from its new posterior end, a second new individual 

 in front of the first formed : the process may be repeated, so that a 

 chain arises, consisting of a parent and several buds, of which the 

 hindmost is the oldest and longest, and that nearest the parent 

 is the youngest (Fig. 136). It will, however, easily be seen that a 

 sharp line cannot be drawn between the fission and budding of 

 Chsetopods ; in both cases certain of the posterior segments of the 

 original individual become a new individual ; in the former a large 

 number of somites pass over into the new animal, in the latter only 



