22 



The Sexual Organization of the Rhizocephala. 



The chief regions of the testis are already differentiated to some extent as soon as the 

 parasite becomes external; it is then possible to distinguish in each testis three regions, (1) the 

 vas deferens, (2) the true germinal region, (3) the region of degenerate hypertrophy. 



The latter two regions are differently situated in Sacculina and Peltogaster (Text tigs. 8 and 9). 



Text fig. 8. 



Text fig. 9. 



In Sacculina (Text figure 8) the germinal region, B-C in the figure, is situated between 

 the vas deferens A-B and the region of hypertrophy E-F, while in Peltogaster Text figure 9) 

 the germinal region, C-D, is situated at the extremity of the testis. The lumen of the testis in 

 young Sacculina does not penetrate to the distal extremity, but in Peltogaster it does so. 



In both cases spermatozoa are only produced by the limited germinal region D-C, while 

 the cells which compose the region of hypertrophy E-F undergo a series of transformations 

 which end in their disintegration. Thus the greater part of the testes undergoes degeneration 

 while only a comparatively small part gives rise to spermatozoa. In consequence it happens 

 that the testes are never at any time full of spermatozoa, the latter being produced in very 

 sparing quantities during the whole life of the parasite. 



The histological changes which take place in the cells of the testes are illustrated in 

 the series of sections on Plate 2 figs. 6 — 14. 



In the germinal region of a young parasite the cells surrounding the central lumen 

 have the character shown in figures 6 and 7. Figure G refers to Sacculina, figure 7 is a lower 

 power drawing of Peltogaster. The cells of the germinal epithelium {gm) divide by mitosis and 

 give rise to a number of smaller primary spermatocytes (sp), which fall into the lumen of 

 the tube. This process takes place when the parasite has been external for three or 

 four days. 



