276 General Biology 



SENSE ORGANS 



The sensitiveness of lumbricus to light and other stimuli is due to 

 the presence of a great number of epidermal sense organs. These are 

 groups of sense cells connected with the central nervous system by 

 means of nerve fibers, and communicating with the outside world 

 through sense hairs which penetrate the cuticle. More of these sense 

 organs occur at the anterior and posterior ends than in any other region 

 of the body. The epidermis of the earthworm is also supplied with 

 efferent nerve fibers which penetrate between the epidermal cells forming 

 a sub-epidermal network. 



THE REPRODUCTIVE SYSTEM 



The earthworm, like Hydra, is hermaphroditic (Fig. 170) 

 ( ), that is, has both sexes in each animal. < 



The female reproductive organs, the ovaries, lie in somite thirteen, 

 the oviducts in somites thirteen and fourteen, while two pairs of seminal 

 receptacles or spermathecae lie in somites nine and ten. 



The ovaries, which are small pear-shaped bodies lying on either side 

 of the mid-ventral line, are attached by their larger ends to the ventral 

 part of the anterior septum. 



The oviducts are made up of various parts. The ciliated funnel lies 

 just posterior to each ovary and passes through the septum, dividing 

 somites thirteen and fourteen, where it has an enlargement known as 

 the egg sac. It then narrows into a thin duct which opens to the external 

 part of the body on the ventral surface near the center of somite fourteen. 



The spermathecae or seminal receptacles are white spherical sacs 

 near the ventral body-wall, one pair each in somites nine and ten. These 

 open to the outside through the spermathecal pores lying between 

 somites nine and ten, and ten and eleven. 



The male reproductive organs consist of two pairs of glove-shaped 

 testes, one pair each in somites ten and eleven. Their positions in the 

 somites are similar to the ovaries. The vas deferens ( ), 



the male organ homologous to the female oviduct, is likewise a ciliated 

 funnel serving as the mouth of the duct through which the sperm pass. 

 This lies immediately behind each testis. The duct itself passes through 

 the septum just back of the funnel, where it forms several convolutions, 

 and then extends backward near the ventral surface. The two sperm 

 ducts which arise on either side of the midventral line, unite in somite 

 twelve and then run back as a single tube, opening to the outside through 

 the spermiducal pore on somite fifteen. In a sexually mature earth- 

 worm, the testes and funnel-shaped inner openings of the sperm ducts 

 are inclosed by large white sacs, the seminal vesicles, which lie in somites 

 nine to twelve. There are three pairs of these sperm sacs, one in somite 

 nine, one in somite eleven, and the third in somite twelve. In somites 

 ten and eleven there are central reservoirs, 



