MANUAL OF ZOOLOGY 



SECT. 



latter the reproductive organs are hermaphrodite and 

 are more complex in structure than in Nereis. There are 

 two special male ducts or vasa deferentia, opening on the 

 ventral surface of the fifteenth segment, and two female ducts 

 or oviducts opening on the fourteenth. 



The fertilised ova of the Earthworm are enclosed, to- 

 gether with a quantity of an albuminous fluid, in a cocoon , 

 the wall of which is formed of a viscid secretion from the 

 glands of the clitellum, hardened and toughened by ex- 

 posure to the air. The cocoon is deposited in the earth, 

 and the embryos develop into com- 

 plete, though minute, worms before 

 they make their escape. At a certain 

 stage the embryos are nourished by 

 swallowing the albuminous fluid con- 

 tained in the cocoon. 



The Earthworms, together with a 

 number of allied fresh-water forms, con- 

 stitute the sub-class Oligochaeta of 

 the Chaetopoda. As a group they are 

 distinguished from the Polychaeta by 

 the sexes being united, by the ovaries 

 and testes being compact and few in 

 number, by the absence of parapodia 

 and cirri, by the non-development of 

 a distinct head-region, and by the absence of a free larval 

 stage. 



Very few Chaetopoda are true parasites ; but a considerable 

 number are to be set down as commensals, habitually asso- 

 ciating with another animal for the sake of food and shelter. 

 The Eartrnvorms burrow in soil containing decaying 

 vegetable matter, passing the mould through the intestine, 

 and subsequently throwing it out in the shape of " castings " 



FIG. no. Lumbricus, 

 setae, highly magnified. 



