EARTHWORM. 



213 



surface there are not a few special apertures, which should be looked 



for on a full-grown worm ; but careful examination of several specimens 



is usually necessary. Almost always plain on the 1 5th ring are the 



two swollen lips of the male ducts, 



less distinct on the I4th are the 



apertures of the oviducts through 



which the eggs pass, while on each 



side, between segments 9 and 10, 



10 and n, are the openings of two 



receptacula seminis or spermatheese 



into which male elements from 



another earthworm pass, and from 



which they again pass out to fertilise 



the eggs of the earthworm when 



these are laid. Each segment 



contains a pair of excretory tubes, 



which have minute ventral-lateral 



apertures, while on the middle line 



of the bade, between the rings, 



there are minute pores, through 



which fluid from the body cavity 



may exude on to the skin. 



FIG. in. Anterior region of 

 earthworm. After Hering. 



Skin and bristles. The Note the eight wtefrO on each segment. 

 . . R.S.) Spots between o-io, 10-11, 



thin CUtlde IS produced by indicate openings of receptacula 



seminis; Ovd., openings of oviducts 

 on segment 14 ; 801, openings of vasa 



deferentia on segment 15. 



the cells which lie beneath, 

 and is perforated by the aper- 

 tures previously mentioned. 

 The epidermis clothing the worm is a single layer of cells, 

 of which most are simply supporting or covering elements, 

 while many are slightly modified, as glandular or mucous 

 cells, and as nervous cells. As the latter are connected 

 with afferent fibres which enter the nerve-cord, the skin is 

 diffusely sensitive. In a few species the skin is slightly 

 phosphorescent. The chitinous bristles, which are longest 

 on the genital segments, are much curved, and lie in small 

 sacs of the skin, in which they can be replaced after 

 breakage. 



Muscular system and body cavity. The earthworm 

 moves by the contraction of muscle cells, which are 

 arranged in circular hoops and longitudinal bands under- 

 neath the skin. The special muscles above the mouth 

 and pharynx have considerable powers of grasping, while 

 less obvious muscular elements occur in the wall of the 

 gut, in the partitions which run internally between the 



