BY DAVID G. STEAD. / ( 



affected, the pleon bearing some resemblance to the female. The 

 appendages of the pleon in this case were wanting, those of the 

 male being rudimentary. As will be at once perceived, the two 

 cases are quite different, as in Neptumis the males are never 

 affected, and the appendages, though modified, are never rudimen- 

 tary; in fact, I have only found a very few isolated examples of 

 the male pleon being at all malformed; and in these it was 

 apparently due to some slight mutilation of the terminal segments. 

 Here, the pleons bore no resemblance to those of the females or 

 the sterile forms, the malformation merely consisting of an 

 aljbreviation of the last two segments, thus partially uncovering 

 the first pair of pleopoda, which were in no wise affected. Prof. 

 A. Giard, in speaking of Sacculina parasitic upon Stenorhyyichus 

 pjialangi'um, says^-' : "In the infested females the influence of the 

 parasite, which displays itself internally by the abortion of the 

 ovules, betrays itself externally by a profound modification of 

 the four pairs of ovigerous feet. These are very inferior in size 

 to the normal state." Now, though the latter part of this agrees 

 with the present case, in A^eptiinus the sterile form possesses an 

 ovary, seminal receptacles and oviducts similar in appearance to, 

 though smaller than, those of the female. The same authority 

 continues : " All these modifications are produced in a more or 

 less complete fashion, according as the crab has been infested at 

 a more or less advanced age." That this does not apply to the 

 present case will be at once evident, when I state that, in speci- 

 mens that I have examined rancfino- from 1 inch to about 5 inches 

 in diameter (including lateral spines) the pleon of the smallest 

 exhibited these modifications in just as marked a manner as the 

 largest, and I have ne^er been able to discover any signs either of 

 Saccidina or any other parasite. 



I have merely quoted these two cases of parasitism to show that 

 in the present instance it is not produced by the same causes. De 

 Haan (Fauna Japonica) figures several species which possess these 



• " Parasitic castration and its influence upon the male sex in the Decapod 

 Crustacea." Ann. Mag. Nat. Hist., (5) Vol. xix. pp. 325-345, 1SS7. 



