100 Mr Potts, Observations on the changes, etc. 



preserve the normal appearance, containing spermatophores in 

 large number with ripe spermatozoa. The genital aperture is 

 never blocked up with chitin as occurs in the cases of extreme 

 modification, and the penis shows no tendency to disappear. In 

 fact it is quite clear that the effect on the reproductive glands is 

 only small — the most noticeable change being the failure of the 

 female to produce large heavily-yolked eggs. The male, it might 

 be supposed, could impregnate the female successfully were it not 

 that the presence of the Sacculina prevented copulation. It would 

 be interesting to observe whether infected males ever attempt the 

 sexual act. 



In summarising emphasis must be laid on the low grade of 

 the modification. One organ only, the abdomen, is subject in the 

 male to a change of a rather striking nature, though the testis 

 continues to produce spermatozoa and the ducts to be filled with 

 spermatophores. It may be pointed out that the term " castration 

 parasitaire," as applied to the phenomenon by Giard, is somewhat 

 misleading here as in other cases, for the modification of the 

 secondary characters is not associated with the suppression of 

 the gonads. 



In Pachygrapsus marmoratus, the common shore- crab of the 

 Bay of Naples, another of the numerous hosts of Sacculina, the 

 modification of the abdomen of infected males is of the degree 

 described above, i.e. about half-way between male and female types. 

 In other respects the change is far greater than that in Garcinus. 

 The female swimmerets appear on the abdomen in more or less 

 complete sets (no mention is made of diminution of the copulatory 

 styles), and the gonads are greatly reduced and may entirely dis- 

 appear. The case of Carcinus is better compared with that of the 

 " stylopised" males of bees {Andrena)* which undergo considerable 

 external change, though throughout parasitism the testis of one 

 side remains fully developed, and produces spermatozoa. 



* Perez. Mem. Soc, Bordeaux, T. iii. 1880, p. xlii. 



