Effects of Castration in Insects 413 



countless eggs while the outer one is of equal size in both sexes, 

 and in both by its paddle-movement maintains respiration cur- 

 rents in the shell. No use has been found for the outer branch in 

 the male and so has become quite rudimentary, but the effect of 

 the parasite Peltogaster is to stimulate the growth of this rudi- 

 ment. There isof course great variabilityof response to this stimu- 

 lus but those individuals which experience the maximum amount 

 of change possess swimmerets exactly similar to those of a mature 

 female, even in the assumption of the curious branched or barbed 

 hairs which in this case can never bear eggs. As in the spider 

 crabs so here, the female appeared incapable of the reverse change, 

 and the large number of hermit crabs with typical female append- 

 ages and sealed genital apertures are undoubtedly to be regarded 

 in part as modified males. 



"A protest will conceivably be uttered against the attribution 

 of a special sexual significance to the development of typical 

 swimmerets in the male in both spider crabs and hermit crabs. It 

 is of course well known that in the larval stages of these Crustacea 

 biramous abdominal appendages are found in both sexes to be 

 subsequently reduced or lost in the male. Lest this, then, be 

 deemed a happy opportunity for applying the term "reversion" 

 to this phenomenon I hasten once more to point out that when the 

 male develops biramous abdominal swimmerets they are of the 

 type associated with female maturity, and that the specialized 

 nature of their nursing-hairs cannot well be associated with ances- 

 tral conditions. 



"Both Sacculina and Peltogaster inflict sterility upon their host 

 and apparently entire abortion of the gonad generally is the final 

 consequence. On the external appearance of the parasite the eggs 

 of the female shrink through absorption of their yolk and the 

 formation of spermatozoa is after a time suspended in the male. 

 The testis of the spider crab dwindles and disappears without 

 undergoing any particular histological change; but in the hermit 

 crab it is curious to note the presence of large cells with large 

 nucleus and abundant protoplasm in sections of the testis. These 

 instantly suggest ova in their appearance and call to mind the 

 instances of the occurrence of such cytological elements as a nor- 



