Chap. XIII.] GONADS OF CRAYFISH. 495 



quite been satisfactorily demonstrated. The distinctions 

 between the various stages of what was originally called 

 parthenogenesis will be considered later on. 



To fix our ideas of the peculiarities of the Arthropod 

 organisation, we may commence with an account of the 

 generative organs of the crayfish ; the testes and ovary 

 are respectively compact glands united along the 

 middle line, and giving only indications of a primi- 

 tively bilateral origin ; they occupy a definite and 

 constant position in the body, lying beneath or just 

 in front of the heart, and having the enteric canal be- 

 neath ; they both give off a duct on either side, which 

 opens to the exterior at the base of one of the paired 

 appendages which are connected with the thorax ; as 

 the female orifice is placed two segments farther for- 

 ward than the male, the oviducts are, as we may sup- 

 pose, shorter than the vasa deferentia which carry 

 away the products of the testes (Fig. 206). 



The cells which line the walls of the ducts of the 

 testes are, at the ends of the final canals, found to 

 occupy swellings, the large cells of which undergo that 

 division into smaller bodies which is so striking a charac- 

 teristic of spermatogenesis ; the products of these 

 divisions are not, however, provided with merely one 

 protoplasmic tail ; in the Crustacea, as in the Nema- 

 tohelminthes, we have a large development of chitin 

 in various parts of the organism, and here, as there, 

 we have spermatozoa developed which are without 

 that protoplasmic flagellar process, which is to be 

 likened to a cilium ; in place of this there are a number 

 of stiff processes, the disposition of which has gained 

 for the spermatozoa the name of "radiate cells." In 

 some Decapoda the rays retain so much of the charac- 

 ter of the pseudopodia of an Amreba that they can be 

 withdrawn into the nucleated portion of the cell 

 (Owsjannikoff). 



Immobile cells like these require some accessory 



