S42 Prof. A. Giavd on Parasitic Castration 



growth and development ; the progenetic animal has conse- 

 quently the aspect of a sexual larva when compared either 

 with the other sex or with allied forms which do not present 

 the phenomenon of progenesis. 



This is in perfect harmony with the principle so well eluci- 

 dated by Herbert Spencer of the antagonism between genesis 

 and groioth and hetween genesis and development. This 

 antagonism is easily explained if w^e consider that the materials 

 employed in reproduction cannot serve for the growth of the 

 individual. If it is advantageous to an animal to reproduce 

 without acquiring useless organs, natural selection will soon 

 determine a more and more complete progenesis. Parasitic 

 animals besides that they draw from their host an abundance 

 of nourishment, have no need of a number of organs which 

 serve their free congeners in their relative life. Thus we see 

 that a very great number of parasitic animals are progenetic. 

 The progenetic males of Bonellia and the Cirripedes live as 

 pjarasites in their females. In certain types (Aphides) pro- 

 genesis ceases wdien, the food becoming less abundant, a 

 change of locality may be necessary. 



In short the arrest of development due to progenesis results 

 from a deflection of the nutritive principles to the detriment 

 of the progenetic animal. In the examples of parasitic cas- 

 tration that we have studied the parasite acts, with regard 

 to its host, absolutely the same part as the genital gland of a 

 progenetic type. It diverts, for its own support, a portion of 

 the principles which should have served for the development 

 of the infested animal. The effects produced are also exactly 

 of the same kind. 



It is curious to observe to what an extent, in certain cases, 

 the parasite seems to take the place of the absent genital 

 products. The Entonisci occupy precisely the position of the 

 sexual glands of the Decapod Crustacea, and so nearly assume 

 their aspect that we have thought we had before us an her- 

 maphrodite of Carcinus mannas, when we had to do with a 

 male bearing a mature Portumon mcenadis. 



The Sacculince and Peltogasters are developed in the very 

 place which the extruded eggs of the crabs and hermit-crabs 

 normally occupy. It is the same with Pkryxus paguri and 

 hij^polytes. I am even much inclined to believe that, by a 

 very singular reflex action, these parasites produce upon their 

 host the same effect that would be produced by oviposition. 

 The Decapods seem, in fact, to defend their parasites against 

 attacks from without. A crab never frees itself from its 

 SaccuUna, even when it has every facility for so doing, and it 

 is only when one places together several Crustaceans bearing 



