LUMBRICUS TERRESTRIS 



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include the ovaries, oviducts, and spermathecse. The ovaries 

 are two small, pear-shaped bodies hanging into the coelom of 

 the thirteenth segment from the septum in front of it. Each ovary 

 is a local thickening of the coelomic epithelium, and is just visible 

 to the naked eye, as a whitish spot (Fig. 122). The broad end of 

 the pear is attached to the septum and contains a fused mass 

 of unripe ova. Ova fall from the stalk into the coelom and are 

 taken up by the oviducts, which lead by wide funnels from the 

 coelom in the thirteenth somite, pass through 

 the septum behind, and open to the exterior 

 in the fourteenth. In the latter somite, each 

 bears a swelling, the receptaculum ovorum 

 or egg sac, in which the eggs are stored and 

 maturation divisions take place. The sperma- 

 thecse are two pairs of small, round sacs 

 which lie in the ninth and tenth somites 

 and open in the grooves behind them. Their 

 function is to receive sperm from another 

 worm. The male organs consist of testes, 

 vesicul3eseminales(seminal vesicles), and vasa 

 deferentia. These testes are two pairs of 

 small, flat, finger-lobed bodies attached to the 

 hinder side of the septa in front of segments 10 

 and II. Like the ovaries, to which they cor- 

 respond in position, they are local thicken- 

 ings of the coelomic epithelium. The testes 

 bud off cells known as sperm-mother-cells, 

 which give rise to spermatozoa in the 

 seminal vesicles. The latter are large sacs, 

 formed by the walling-off of parts of the coelom, which enclose 

 the testes. Each consists of a median part and lateral horns. 

 The anterior seminal vesicle, in segment 10, has four lateral 

 horns, two in front and two behind, which push out the septa 

 and bulge into the ninth and eleventh segments. The posterior 

 seminal vesicle in segment 11, has only two such horns, which 

 project into the twelfth segment. Each sperm-mother-cell forms 

 by multiple fission, in the course of which the usual reduction 

 division takes place, a mulberry-hke mass (Fig. 123), consisting 

 of Httle cells attached to a central mass of residual protoplasm 

 known as the cytophore, by which they are nourished. The little 

 cells become pear-shaped, with the broad ends on the cytophore, 



Fig. 122. — One of the 

 ovaries of an earth- 

 worm. 



