Metazoa Lumbricus. 247 



its own ova. The fertilising sperms are obtained from 

 another worm, and stored in four small spherical sacs, or 

 spermathecae, which open one pair between the ninth and 

 tenth, and the other pair between the tenth and eleventh 

 somites. 



Passing now to the male organs we find that the sperm- 

 aria are, like the ovaria, microscopic bodies attached to 

 the mesentery. There are two pairs of spermaria, and they 

 lie on the posterior sides of the septa, separating the ninth 

 and tenth, and the tenth and eleventh somites. The sperms 

 are, however, not sexually mature when they leave the sperm- 

 aria. They are known as spermospores from which sperms 

 are afterwards formed by a process of budding. This further 

 development takes place in large irregular organs known as 

 vesieulae seminales, or seminal reservoirs (fig. 123). The 

 vesiculse seminales are four in number, two on either side 

 of the ventral middle line, and occupy the cavities of the 

 tenth and eleventh somites, growing forwards and backwards 

 when fully developed into the ninth and twelfth somitic 

 spaces. The spermaria are found fully developed only in 

 young worms, and the vesiculae seminales, though present 

 along with the spermaria, attain a large size only in the adults. 



The fully developed sperms, each consisting of along, rod- 

 shaped head and flagellum, are conveyed to the exterior by 

 four wide- mouthed delicate sperm -ducts, or vasa deferentia. 

 The mouths of the vasa deferentia open on the anterior 

 faces of the septa immediately behind those to which the 

 spermaria are attached. The ducts in continuation with the 

 funnels run backwards, the two vasa deferentia on either 

 side fusing and opening by one aperture on the ventral wall 

 of the fifteenth somite, the somite immediately behind that 

 on which the oviducts open. 



Fertilisation and development. The ripe ova, on their 

 escape from the oviducts, are fertilised by sperms (of another 

 worm) squeezed out of the spermathecal openings. The 

 fertilised ovum, or embryo, is then enclosed in a chitinous 



