610 F. A. POTTS. 



itself any time within the first fifty days of adolescent life, 

 and yet be able to check the complete development of the 

 female type of appendage/' But the parasite does not exert 

 its retarding stimulus directly after fixation, and we are 

 without data which would give the period after which it 

 commences to do so. To support this explanation of 

 the apparent modification of the female characters, it is 

 probably necessary to postulate a larval infection. During 

 the last moults of larval life the Peltogaster would remain in 

 the internus stage and in the time of the first adolescent 

 moults, whether or no its stage of development was suffi- 

 ciently advanced for an external appearance, the checking 

 effect on the further development of the female appendage 

 could be brought about. 



Assuming then that the course of development runs fairly 

 similarly in Eupagurus longicarpus and meticulosus, 

 it is perfectly open to consider the exceptional cases men- 

 tioned above as due to unusually early, probably larval, 

 infection and consequent midway arrest of the assumption of 

 the female characters. That this is the true explanation of 

 the phenomenon is indicated by the unusually small size of 

 the infected individuals and by the fact that the develop- 

 ment of the first appendage was more distinctly female than 

 the other two. It will be later seen from other evidence that 

 the parasitism does not cause alteration in the once assumed 

 female characters. 



Effect on the Secondary Sexual Characters op 

 Eupagurus prideauxi. 



Before proceeding to describe the effect of parasitism on the 

 primary sexual characters of Eupagurus meticulosus it 

 will be well to mention the conclusions gleaned from the small 

 amount of infected material of E. prideauxi I have been able 

 to collect. This species differs from E. meticulosus in the 

 complete absence of the abdominal appendages of the second. 



