3. The Case of Eriphia spinifrons. 77 



cellanae. Now if the simultaneous occurrence of Lernaeodiscus and Entoniscus on one and the 

 same crab is simply a matter of chance we should expect only 4 crabs out of the 1000 exam- 

 ined to be simultaneously infected; but Ml'ller found that 21 out of the 1000 carried both 

 Lernaeodiscus and Entoniscus. 



Giard & Bonnier (1. c.) have confirmed this observation with reference to Portunion 

 maenadis and Sacculina carcini, parasites of Carcinus maenas, and to Portunion salvatoris and 

 Sacculina si?nilis, parasites of Portunus arcuatus : but the number of parasites observed in neither 

 case was very large. 



The case which is here to be described concerns the parasites of Eriphia spinifrons, 

 neither of which have been hitherto described as far as I am aware. The Rhizocephalous 

 parasite of Eriphia spinifrons is very similar to the parasite of Pachygrapsus marmoratus which 

 Kossmann calls Sacculina benedeni. The Entoniscid parasite of Eriphia spinifrons has not been 

 notified hitherto; I am unable to give a diagnosis of it since my observations on it are con- 

 fined to the adult state when all specific distinctions have disappeared. The fact that 

 Eriphia spinifrons is infected by a species of Entoniscid was revealed to me in a most 

 curious way. 



Dr. Duncker in the course of his investigations on correlation in Eriphia spinifrons at 

 Naples made some incidental notes with regard to the occurrence of Sacculina on this species, 

 with a view to testing Giard's theory of parasitic castration. The facts which he elicited 

 were of so peculiar a kind that he was led to believe that they constituted a most antago- 

 nistic piece of evidence to Giard's theory: learning that I was specially interested in this 

 subject he handed over his notes and some most valuable material to me, the examination of 

 which has led to the discovery in question. Dr. Duncker investigated 2601 specimens of 

 Eriphia spinifrons of which 63 carried external Sacculinae. Now the whole array of crabs 

 fell into three sharply distinguished categories, namely males, females and hermaphrodite forms. 

 The males are distinguished sharply from the females by the narrowness of the abdomen and 

 the fact that the latter are furnished only with a pair of copulatory styles while in the female 

 the abdomen is broader and carries four pairs of ovigerous appendages. The hermaphrodite 

 forms belong to a compact and easily distinguished category; the abdomen is nearly as broad 

 as in the female which it further resembles in colour and in the presence of fringing hairs, 

 but instead of having the ovigerous appendages of the female it possesses a pair of copulatory 

 styles. The three types of abdomen are shown in dorsal and ventral view in the Text fig. 21 A — F 

 [AD = male, BE = female, CF = hermaphrodite). 



The 66 crabs infected with Sacculina were distributed among these three categories in 

 the following manner. 



Males Females Hermaphrodite 



Total number 1354 1200 47 



Number of crabs infected with Sacculina 16 31 1 6 



