REPRODUCTIVE ORGANS. 75 



however, is surrounded witli still smaller cells constitutiii*'- its 

 nutrient envelope or follicle. As the ova mature the follicles 

 still persist, and they may be detected even in the ci^j^sti-iiiir. 

 When fully ripe the ovum bursts the follicle and is shed from 

 the end of the egg-string into the body-cavity. It is ultimately 

 taken into the oviduct and carried to the exterior. 



The development of the ovary shows it to be morphologically 

 a thickening of the peritoneal epithelium. The eggs therefore 

 are originally epithelial cells. 



The sjjennaries or testes {t,t, Fig. 29) are four in mnnl)eraiid 

 in outward appearance are somewhat similar to the ovaries. 

 They are small ilattened bodies with somewhat irregular or lohed 

 borders, lying one on either side the nerve-cord in a position 

 corresponding with that of the ovaries, but in somites 10 and 11. 

 Like the ovary the testis is a solid mass of cells, which are shed 

 into the body-cavity and are finally carried to the exterior. 

 The sperm-cells leave the testis, however, at a very early period 

 and undergo the later stages of maturation within the cavities of 

 the seminal vesicles described below. 



Accessory Reproductive Organs. The most important of the 

 accessory organs are the genital ducts, by which the germ-cells 

 are passed out to the exterior. Both the female ducts {oviducts) 

 and the male {sperm-ducts) are tubular organs opening at one 

 end to the outside, through tlie body-wall, and at the other end 

 into the coelom by means of a ciliated funnel somewhat similar 

 to a nephridial funnel, but nnicli larger. By means of these 

 ciliated funnels the germ-cells after their discharge t'runi the 

 ovary or testis are taken up and passed to the exterior. 



The oviducts {od, Fig. 29, Fig. 23) are two short trumpet- 

 shaped tubes lying innnediately posterior to the ovaries and p;uss- 

 ing through the dissepiment between the 13th and 14th somites. 

 Tlie inner end opens freely into the cavity of the 13th somite, 

 by means of a wide and much-folded ciliated funnel, fi-om the 

 centre of which a slender tube passes backward througli the 

 dissepiment, turns rather sharply towards the outer side and, 

 passing through the body-wall, opens to the outside on the 14th 

 somite (see p. 43). Innnediately behind the dissepiment the 

 oviduct gives off at its dorsal and outer side a small ])oueh, 

 richly supplied with blood-vessels. In this, the receptacul um 



