ANNELIDA 



303 



developed orienting apparatus, are especially well adapted to a free life. 

 They swarm about and secure the necessary distribution of the sexual 

 products, whereas the less active budding form remains at the bottom of 

 the sea. The extensive development of the parapodia is completed even 

 while the buds are still connected with the parent. This recalls the 

 condition of certain Nereidce, in which new setas, better adapted to 

 swimming, make their appearance on the posterior part of the body at 



Fig. Ul.— Part of a stock of Si/lUs ramosn (somewhat diagrammatic, after 

 McIntosh, and from a j reparation of the Challenger material), d, intestine, 

 which branches throughout the entire stock. The stock is injured in some places. 



the time of sexual maturity {epitokal form) ; these give to the sexually 

 mature animals an entirely different appearance from that of the young 

 form (so-called atokal form), so that here also the sexually mature and 

 the young forms were assigned to different species and genera. In the 



