in the Decapod Cni.tfacea. 335 



In general a stylopized bee has the head smaller than a 

 normal individual of the same species, the abdomen more 

 globose, the integument of this latter organ sometimes dis- 

 coloured, its puncturing less strongly marked, its villositj more 

 abundant and longer upon the last segments, and presenting a 

 marked tendency to acquire a golden-red tinge towards the 

 extremity in those species in which the hairs of this part are 

 fulvous or even brown. Lastly, which is even more remark- 

 able, the female has tlie hind legs more slender, and their 

 brush more or less reduced, sometimes wanting ; and in the 

 species in which the male has the face white or yellow tlie 

 female acquires spots of this colour ; the sting itself becomes 

 smaller. On the otlier hand, the male sometimes loses the 

 proper coloration of his face, and thus becomes more like the 

 female. Each sex thus loses more or less the attributes which 

 characterize it and tends more or less to acquire those of the 

 opposite sex. 



It must be added that a stylopized female is never seen 

 bearing pollen on the hind legs ; she plunders the flowers, but 

 only for her own nourishment, and not to collect anything. 

 She therefore appears to be destitute of the reproductive func- 

 tion, as she is deprived of certain characters which are the 

 external signs of it. 



It was natural to deduce from these facts that by its 

 presence the Stylops causes the atrophy of the internal 

 genital organs. Some authors who have paid attention to 

 parasites have, in fact, noted in passing the atrophy of the 

 genital organs of the host. But these data are very vague 

 and it was necessary to check them. M. Perez ascertained 

 that in a stylopized female Andrena the ovarian tubes are 

 completely arrested in their development and the ova never 

 attain their normal evolution ; the stylopized female is unfitted 

 for reproduction. In the male the atrophy usually affects 

 only the testis of the side on which the parasite is situated ; 

 the sperm-cells become segmented, but without producing 

 spermatozoids. But the testis of the opposite side attains 

 its normal volume and is found to be distended by a great 

 quantity of semen. The stylopized male may therefore still 

 copulate with effect ; the stylopized female probably never 

 copulates — at any rate she cannot lay fertile eggs. 



According to Perez this atrophy of the genital organs is a 

 simple arrest of development and appears to be chiefly an 

 effect of the pressure due to the presence of the parasite, whose 

 body almost entirely fills the abdomen*. 



* To the examples of parasitic castration above enumerated we may 

 further add the very interesting case of the North-American squirrel, 



