188 



ZOOLOU V 



V- 



\i 



-V 



'\ 



;V 



duction is rcmarkalile. The same method, however, occurs 

 in different guises in many other free-hving annelids. In this 

 form the paddles or parapodia at the anterior hrdf of the 

 animal are different from those at the posterior half, for the 

 latter are large and fitted for s^^•imming. 

 Eventually one of the middle segments of 

 tlie Ijodv Ix'comes transformed into a head, 

 bearing eyes and tentacles; then the whole 

 of the hinder half lireaks off "of itself." 

 The newh' formed head is now the head 

 end of the new individual. This indi\'id- 

 ual leads a different kind of life from the 

 half which remains in the tube, for it 

 swims freely in the water. The separated 

 individuals are either male or female, 

 whereas the part \A-hich lives in the tube 

 never produces eggs, but merelj' forms a 

 new tail CA'cry time the old tail is cut off 

 to form a sexual individual. 



We have now to consider the non-loco- 

 motor or sedentary Polycha?ta. The first of these is not 

 greatly changed from the free-living type. This is Clj'- 

 menella (Fig. ISO), which looks like a reddish, jointed 

 straw. It builds tuljcs of agglutinated sand in which it 

 spends much of its life. Parapodia occur on each segment, 

 but they are v'cry small. Ampliitrite (Fig. 181) builds firm 

 tubes of sand. Its parapodia are ruflimentary Ijehind. The 

 function of respiration is carried on by three pairs of parapodia 

 which are borne on the head. These are immensely enlarged, 

 forming l)lood-red gill tufts. Amphiti'ite has many close 

 allies that show different stages of degeneration. Thus the 



Fig. 180. — C'l>Tnonella, 

 straw-worm. The an- 

 terior segments oiil>' 

 are shown. After M. 

 Lewis. 



