36 PRIMITIVE ANIMALS 



the alimentary canal, blood-vessels and nerve-cord 

 really lie outside the coelomic cavity, being covered 

 over with a layer of coelomic epithelium. They pro- 

 ject into the coelom, but they do not lie in its cavity. 



There are however two sets of organs which 

 actually lie in the coelomic cavity, and always bear 

 a very intimate relation to it. These are the ex- 

 cretory and reproductive organs respectively. 



The reproductive cells, ova and spermatozoa, are 

 derived actually from the coelomic wall, and the 

 reproductive organs, ovaries and testes, are simply 

 specialized parts of the coelomic cavity engaged 

 in the elaboration of the sexual products. Intimately 

 related with these organs, funnels may be developed 

 connected with a coiled duct leading to the exterior. 

 These are the genital funnels for conveying the 

 sexual products to the outside of the body, and since 

 they too are developed from the coelomic wall they 

 are called coelomoducts (Fig. 3 .st.). In some worms 

 a pair of these coelomoducts and reproductive organs 

 may be developed on a very large number of seg- 

 ments, but in other cases, as in the Earthworm, they 

 may be restricted 'to a few segments. 



The excretory organs in the Earthworm consist 

 of a pair of coiled tubes in each segment, each with 

 a ciliated funnel opening into the coelomic cavity, 

 and a duct opening to the exterior (Fig. 3 neph.). 

 These are the nephridia which collect the waste 



