GENERAL ORGANOLOGY. 



117 



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

 the nephridial tubes becomes specially close by the development 

 of the glomeruli (Malpighian corpuscles); bundles of capillaries 



fe 



N* M 



FIG. 69. 



FIG. 69. Segmental organ of an Oligochaete. (From Lang.) fz, ciliated funnel ; dis, 

 septum ; ng l , non-glandular, tig' 1 , 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 (W); Ns, nephrostome ; M, Malpighian bodies of the seg- 

 mental tubules (S). 



carrying the walls of the 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 the germinal cells are produced, 

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

 are present, temporarily or permanently, in all multicellular 

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

 If the sexual products arise in the skin or in the walls of the 

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



