METAZOA VERMES. 307 



ANNELIDA. HIRUDINIA. 



Some of the non-parasitic members of this class resem- 

 ble the Oligochaeta. Nephelis (PL 761, the young), for 

 example, is cylindrical in form similar to the earthworm, 

 and its suckers are smaller than in most members of its 

 class. Its intestine is not differentiated into numerous 

 large sacs as is the case with the more specialized Hiru- 

 dinia to be hereafter described. 



The eggs of Nephelis are deposited in cocoons in 

 fresh water, but the adults often leave the water and live 

 under stones on the shore. 1 



The land leech, Haemadipsa japonica (PI. 762, fig. i, 

 at rest, dorsal view; fig. 2, ventral view; fig. 3, another 

 worm stretched out, dorsal side ; all natural size), lives 

 in moist places among mountains and never goes to the 

 water, not even to lay its eggs. As in all leeches the seg- 

 ments are ringed, making it difficult to determine the 

 exact number (fig. 4, posterior, and fig. 5, anterior end, 

 both figures enlarged). A shortening of the body at 

 either end has taken place in Haemadipsa, as in most 

 land leeches, brought about by a reduction of the number 

 of rings in a segment. 



The eggs of the European medicinal leech, Hirudo 

 medicinalis Linn, (in America, Macrobdella decora Say, No. 

 763, is often used in place of Hirudo), are laid in cocoons 

 which are placed in holes that the mother has made 

 above water level in the soft, moist banks of the pond 

 she inhabits. The cocoon usually contains about twenty 

 eggs and is filled with albumen. The young remain in 

 the cocoon, feeding upon the food prepared for them until 

 they have attained the form of the parent. The free- 

 swimming larval stage is therefore omitted, so that the 

 development is accelerated. 



1 Johnston, Cat. Worms Brit. Mus., 1865, p. 43. 



