HERMIT CRAB AND PELTOGASTER. 613 



males (pi. 34, fig. 2) regenerate appendages in wliich tliey are 

 manifestly unequal, and in which at first, indeed, only the 

 external ramus may be developed. 



In those on which the Peltogaster was allowed to remain 

 the interesting fact was observed that a female with an 

 abdominal appendage removed regenerates one of purely 

 female type, and this, together with the evidence derived 

 from moulting, seems entirely to prove that the Peltogaster, 

 at least in the later stages of parasitism, exerts no influence 

 at all on the secondary sexual characters of the female, or on 

 the processes which regulate their reformation. So also with 

 regard to the male it appears that the modifying cause 

 operates at an early stage in the history of infection, and 

 that the degree of modification is not subsequently increased. 

 I am inclined to attribute the great variability in degree of 

 modification in infected male crabs to constitutional differ- 

 ences in the crabs themselves, not to date of infection, for 

 the same range of variation is found in crabs of all sizes, nor 

 to the comparative vigour of the Peltogaster, for quite large 

 Peltogasters may be present on unmodified, and small Pelto- 

 gasters on modified, hosts. 



The permanence of modification in recovering crabs may be 

 compared with a kindred phenomenon in Mammalia. In 

 deer the females may assume the horns characteristic of the 

 male, as a consequence of atrophy or disease of the genitalia. 

 But cases are known of female deer with horns which, on 

 dissection, showed normal ovaries. Herbst (4) refers the 

 growth of the horns to a period when the ovaries were in a 

 diseased condition, but while these later recovered their 

 normal state, the modification of the secondary sexual 

 characters remained. 



VOL. 50, PART 4. NEW SERIES. 44 



