STRUCTURE OF THE EARTHWORM. 171 



probably get finer .waste-products from the associated blood- 

 vessels. Nephridia occur in many animals, in most young 

 Vertebrates as well as among Invertebrates, but they are 

 never seen more clearly than in the earthworm. When 

 a nephridium is carefully removed, along with a part of the 

 segment septum through which it passes, and examined 

 under the microscope, the following three parts are to be 

 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 

 particles 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 consists in part at least of a series of intra-cellular 

 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. The nephridia usually lodge 

 minute parasitic Nematodes. 



Reproductive System. — The earthworm is hermaphrodite, 

 and its reproductive organs are somewhat difiScult to de- 

 monstrate with completeness. To see them it will be neces- 

 sary to dissect several earthworms with special attention to 

 the several parts. 



(a) The Male Organs consist of a pair of testes, three 

 pairs of seminal vesicles, and a paired vas deferens. 



(i) The testes lie near the nerve-cord on the septa between 

 segments 10 and 11 ; each is "a white translucent body 

 of irregular quadrangular form, rarely more than one-tenth 

 of an inch in diameter." They will not be found by the busy 

 student. 



(2) Mother-sperm-cells, which give rise by division to 

 young spermatozoa, pass from the testes to the much 

 lobed seminal vesicles, where the spermatozoa are ma- 

 tured. These seminal vesicles are very prominent, and 

 seem to be outgrowths of the septa between segments 

 nine to twelve. Among the spermatozoa there are para- 

 sitic Gregarines {Monocystis) in various stages of develop- 

 ment. 



(3) The spermatozoa pass from the seminal vesicles into 

 two vasa deferentia or male ducts. These open to the 

 exterior on the isth segment. Each vas deferens bears 



