Effects of Castration in Insects 415 



comparatively small number of cases with fully formed herma- 

 phrodite glands we are not going too far in definitely asserting a 

 connection between their occurrence and parasitic influence, for 

 bisexual gonads have to my knowledge never been met with in 

 Decapod Crustacea under normal conditions.*^ But it thus ap- 

 pears that the curious condition in the hermit crab is an incipient 

 stage corresponding to the perfect hermaphroditism of the "re- 

 covered" spider crabs, and if the action of the parasite in absorb- 

 ing surplus nutrition were withdrawn the voung ova in the testis 

 of the hermit crab would become large and pigmented like those in 

 the spider crab. 



"These two cases have been described at some length as ex- 

 amples of extreme modification. In other Decapod Crustacea 

 which are infected by the same parasite an effect is observable 

 which is similar in kind but not in degree. The common shore 

 crab of England (Carcinus) is commonly aflflicted (if affliction it 

 be) by Sacculina. Here again the male undergoes modification 

 while the reverse change never occurs in the female. The narrow 

 abdomen of the male is often exchanged at the moult after infec- 

 tion for one much broader but never attaining the full female 

 width. One may look in vain, however, for anv reduction of the 

 copulatory styles or for the appearance of the smallest rudiments 

 of swimmerets. The closure of the genital apertures nearly al- 

 ways follows parasitic attack in spider crab and hermit crab; but 

 they never become blocked up in shore crabs with Sacculina. Yet 

 the external change is apparently greater than that produced in the 

 reproductive glands. Dissection in every parasitized male showed 

 vasa deferentia of the characteristic milky white color due to 

 countless masses of spermatophores all packed with spermatozoa. 

 The testes though reduced, then, always remain in reproductive 

 activity. The parasites which infect sp'der crab and shore crab 

 are practically identical and presumably exert a very similar stim- 

 ulus yet the results are markedly different. It is obviously the 

 host which offers a different reaction in the two cases. In another 



* In a footnote Potts states that "Caiman in the recently appeared volume Crustacea of Ray Lan- 

 kester's Treatise on Zoology refers to the unpublished observations of Wolleback on normal hermaphrod- 

 it'sm in certain deep-water Decapoda." 



