32 EARTHWORMS AND LEECHES [CH. I 



parent by their posterior suckers for some time. Another 

 common leech, Clepsine complanata 1 , which preys on water 

 snails such as Planorbis, nurtures the young in a similar 

 way : here the eggs pass from the genital aperture in two 

 longitudinal rows back to the hinder portion of the body 

 which is looped up into a pouch to receive them and to 

 constitute a brood chamber until the young hatch and 

 fasten themselves to the ventral surface of the parent by 

 their suckers. 



Dispersal. In addition to the locomotive powers of the 

 adult leeches whereby they can travel both in water and 

 for short distances over land, currents and floods doubtless 

 play an important part in carrying the eggs to fresh places. 

 These modes of dispersal can hardly account for the wide 

 distribution of many species; this has probably been 

 effected by the aid of the animals on which the leeches 

 prey. They have been seen clinging to the legs and other 

 parts of cattle and horses that have entered the water to 

 drink, and also to the legs and feet of water birds and 

 waders, by whose agency they might well be carried to 

 ponds and streams distant several miles in a few minutes. 

 Moreover the mud adhering to the feet of such birds and 

 mammals might at times contain in it eggs whose de- 

 velopment would be in no way impaired by transport to 

 other waters. 



1 Brightwell, loc. cit. 



