x PHYTLUM ANNUL AT A 425 



to open by the corresponding male aperture on the fifteenth 

 segment. 



The female reproductive organs consist of a pair of ovaries, a 

 pair of oviducts with a pair of receptacula ovorum, and two pairs of 

 receptacula seminis. The ovaries (ov.) are minute pear-shaped bodies, 

 which are situated in the thirteenth segment, attached to the 

 septum between the twelfth and thirteenth. The oviducts (ov. d.) 

 are a pair of short tubes, each with a comparatively wide funnel- 

 shaped opening into the cavity of the thirteenth segment, and 

 extending backwards and outwards in the fourteenth segment, to 

 open at the female aperture on the ventral surface of the latter. 

 The receptacula ovorum are a pair of reniform sacs which open into 

 the funnel-shaped ends of the oviducts. The receptacula seminis 

 (rec.) are two pairs of rounded sacs which open on the exterior 

 in the intervals between the ninth and tenth, and tenth and 

 eleventh segments. 



Though hermaphrodite the Earthworm is not self-impregnating, 

 but two individuals provide for mutual fertilisation by an act 

 of copulation. The copulating individuals become applied together 

 by their ventral surfaces, the heads pointing in opposite directions, 

 and become attached in this position by the seta?, of the genital 

 region and by a viscid secretion from the clitellum and of certain 

 glands, called the capsulogenous glands, situated in the neighbour- 

 hood of the reproduction organs. The sperms from the male 

 apertures of each pass along temporarily formed grooves to the 

 receptacula seminis of the other. 



When the ova are mature they are discharged from the ovary 

 into the cavity of the thirteenth segment, whence they pass out 

 to the exterior through the oviduct, to be enclosed in the cocoon, 

 after having been detained for a time in the receptaculum 

 ovorum. 



Development. The oosperms or fertilised ova of the Earthworm 

 are enclosed, together with a quantity of an albuminous fluid 

 derived from the capsulogenous glands, in a cocoon, the wall of 

 which is formed of a viscid secretion from the glands of the 

 clitellum, hardened and toughened by exposure to the air. The 

 cocoon is deposited in the earth and the embryos develop into 

 complete, though minute, worms before they make their escape. 

 The segmentation is somewhat unequal. A flattened llastula 

 (Fig. 335.4) is formed, with a large but flattened segmentation 

 cavity. This becomes invagmated to form a cylindrical gastrula 

 (B) : the blastopore becomes narrowed and subsequently gives 

 rise to the mouth of the adult. A pair of large mcsodcrm cells 

 (m) early become marked off from the other cells of the gastrula ; 

 these become divided to form a pair of mesoderm l>ands composed 

 of several rows of small cells, which grow forwards towards the 

 month. By swallowing movements the embryo at this stage takes 



