252 



PHYLUM ANNELIDA 



the microscope, the following three parts are seen : — 

 (a) An internal ciliated funnel ; (b) a trebly coiled ciliated 

 tube, at first transparent, then glandular and granular ; and 

 (c) a muscular duct opening to the exterior. Minute par- 

 ticles swept into the ciliated funnel pass down the ciliated 

 coils of the tube, and out by the muscular part which opens 

 just outside of the ventral bristles. The coiled tube con- 

 sists in part at least of a series of intracellular cavities, that 

 is to say, it runs through the middle of the cells which 

 compose it ; the external muscular portion arises from an 

 invagination of skin. 



Reproductive system. ^ — Like all Oligochaetes,the earth- 

 worm is hermaphrodite and the organs complex. The 

 complexity is produced by the specialisation of certain of 

 the nephridia to form genital ducts and accessory organs, 

 and by the presence of chambers (seminal vesicles) con- 

 nected with the testes, formed by the shutting off of 

 portions of the body cavity. 



The organs in the earthworm are difficult to dissect, and 

 differ considerably in old and young specimens. 



(a) The Male Organs consist of two pairs of testes, three 

 pairs of seminal vesicles, and paired vasa deferentia. 



(i) The testes, flattened lobed bodies, about ^\, in. in 

 size, arise from proliferations of the peritoneal lining of 

 the body cavity, and are invested by a delicate membrane 

 derived therefrom ; they lie near the nerve-cord, attached 

 to the posterior surfaces of the septa between segments 9-10 

 and lo-ii. They are minute, translucent, and difficult 

 to see. In immature worms they lie exposed in the body 

 cavity ; in mature worms they are concealed by the great 

 development of the seminal vesicles. 



(2) The seminal vesicles are much-lobed structures, 

 exceedingly prominent in dissection. Small and laterally 

 placed in young worms, in the adult the anterior two 

 pairs fuse in the middle line and cover the anterior pair 

 of testes and their ducts, while the posterior pair similarly 

 conceal the second pair of testes with their ducts. Into the 

 seminal vesicles mother sperm cells from the testes pass, 

 and divide up to form spermatozoa. 



Development shows that the seminal vesicles arise as 

 outgrowths of the septa of segments 9-12, and that their 



