hi the Decapod Crustacea. 333 



a phenomenon of correlation of growth without any direct 

 mechanical cause. 



I should have liked to pursue the observation of these 

 curious facts in other species of Decapods infested by Entione ; 

 unfortunately these parasites are rare, and PlotyonycJius latipes^ 

 which is very frequently infested by Portunion Kossmanni at 

 Wimereux, is not well adapted for the investigation of this 

 question in consequence of the narrowness of the abdomen in 

 both sexes. 



Taking into account the facts which we have just discussed 

 we may inquire whether the peculiarity noticed by Rathke, 

 to which we have already referred, namely the exclusive in- 

 festation of the female prawns by Bojnjrus squillarum^ may 

 not be explicable by a mistake analogous to that which we at 

 first fell into with regard to the Sacculina of Stenorliynchus. 



Rathke also first indicated, and all subsequent authors have 

 confirmed this statement, that the presence of a Bopyrus caused 

 the sterility of the prawn which bore it. He says : — " Hand 

 minus memoratu dignum hoc mihi videter, quod neque 

 eo anni tempore quo Paljemones ova sua (sub cauda) fovent, 

 neque uUo alio tempore inter ea horum anim.alium exempla, 

 qute Bopyrum exceperant, ullum inveni cujus ova ita exculta 

 fuissent, ut partu edi potuissent " *. 



But the external characters which distinguish the sexes in 

 Palcemon are not very striking. Grobben +, who has recently 

 studied this questionpretty completely in the case oi Palcemon 

 rectirosti'is, ascribes to the male the following differential 

 peculiarities : — 



1. Its size is smaller. 



2. The inner branch of the first pair of abdominal feet is 

 much more developed than in the female. 



3. The second abdominal foot bears on the inside of its 

 inner branch a styloid appendage furnished with stiff hairs \. 



4. The branch of the first antennse which bears the olfactory- 

 setae is larger than in the female, and that absolutely and not 

 only relatively to the size of the body. The olfactory setae 

 are also more numerous. 



As the Bopyridaj generally infest the young Decapods, the 

 first character (1) derived from the size cannot be of any use 

 in the question now under consideration. The other charac- 

 ters consist in the greater development in the male of organs 



• Eathke, De Bopyro et Nereide, 1837, p. 18. 



t Grobben, ' Beitriige zur Kenntniss der maunliclier Geschlechtsorgane 

 der Dekapoden ' (Vienna, 187C)), pp. 76, 77, 79. 



\ Heller further indicates a second and smaller inner appendage, but 

 he has mistaken for this the retinaculum (' Die Crustaceen des sudlichen 

 Europa,' Vienna, 1808). 



