60 THE EARTH-WORM 



14th segments, and opens to the exterior by the female genital aperture on 

 the 14th segment. 



The vesiculse seminales or sperm-sacs lie above the nerve cord in segments 

 9 to 12, and completely cover in the testes and the internal openings of the vasa 

 deferentia. Each seminal vesicle consists of two parts, a spacious median un- 

 paired sac or sperm-reservoir, and paired lateral expansions of these, the seminal 

 vesicles proper. These expansions are seen on opening the worm, appearing as 

 three pairs of sacs at the sides of the alimentary canal. The anterior median 

 seminal vesicle lies in the mid-ventral part of the 10th segment ; and its four 

 comers are produced into pouches, the pair of anterior lateral seminal vesicles,, 

 which extend from the 10th segment and occupy the cavity of the 9th, and the 

 first pair of posterior lateral seminal vesicles, which push backwards and occupy 

 the cavity of the 11th segment. The posterior median seminal vesicle lies in 

 the mid- ventral part of the 11th segment, and it has only one pair of pouches 

 — namely, the second pair of posterior lateral seminal vesicles, which extend 

 so far back as to occupy the 12th and 13th segments. Carefully remove the 

 vesicles of one side so as to expose the testes and the internal funnels of the 

 vasa deferentia. 



The testes are two pairs of small bodies attached, on either side of the nerve 

 cord, to the posterior faces of the septa separating the 9th and 10th and the 10th 

 and 11th segments. Inmiediately behind each testis lies a large ciliated funnel, 

 the internal opening of a seminal duct. On each side the seminal duct of the 

 anterior testis passes backwards through the septum separating the 11th and 

 12th segments, and is joined in segment 12 by the seminal duct of the posterior 

 testis. The two ducts form the vas deferens, which passes through the successive 

 septa to segment 15 and there opens to the outside by the male genital aperture. 



In the 9th and 10th segments there is a pair of small white spherical sacs, 

 the spermathecse or receptacula seminis, opening by pores between segments 

 9 and 10, and 10 and 11. 



Make a complete sketch showing as much as possible of the reproductive 

 and nervous systems. 



Transverse Section of Body. 



In a transverse section of the body of the Earth-worm the following 

 structures Avill be seen : — 

 (a) The thin cuticle. 

 (6) The epidermis, consisting of a single layer of cells. 



(c) The dermis, a very thin layer of connective tissue. 



(d) The circular muscles. 



(e) The longitudinal muscles, arranged into seven bundles. 



(/) The setas or chaetas, situated in special setigerous sacs formed from the 

 epidermis. 



(g) The coelome or body-cavity, the space between the body-wall and the 

 alimentary canal. 



(h) The intestine, which is coated externally with the " yellow-cells " or 

 coelomic epithelium. It has a deep dorsal fold, the typhlosole, pro- 

 jecting downwards into the cavity of the intestine. This fold is filled 



