GENERAL OROANOLOOT. 



117 



tion of the nephrostomata. The relation of the blood-Tessels to 

 the nephridial tubes becomes specially close by the development 

 of the glomeruli (Malpighiau corpuscles); bundles of capillaries 



Ns J/ 



Fig, 69. 



Fig 



. 69.— Segmental organ of an Oligochaete. (From Lang.) tz, ciliated funnel ; rlia 

 septum ; iiy', non-glandular, ?i(/^ glandular, part of the canal ; eh, terminal ves- 

 icle; In, body-wall. 

 Fig. 70.— Diagram of the primitive kidney of a vertebrate. (From Hatschek.) Dotted 

 lines mark the limits of the segments. A, anal opening; P, mouth of the duct of 

 the primitive kidney (ID; JVs, nephrostome; M, Malpighian bodies of the seg- 

 mental tubules (S). 



carrying the walls of tlie canal before them and so projecting into 

 the lumen of the tube. 



B. Sexual Organs. 



Sexual Glands and Ducts. — In the sexual apparatus of animals 

 are distinguished the areas where tlie germinal cells are produced, 

 tlie sexual glands or gonads, and the ducts for tliese. The former 

 are present, temporarily or permanently, in all multicellular 

 animals; the latter, on the contrary, may be completely absent. 

 If the se.xiuil products arise in the skin or in the walls of the 

 digestive tract, as is usually the case in the ccelenterates, then 



