EPIZOA AND PARASITES 



237 



The epicarid larva was obtained from the marsupium of a female. Cryptoniscid 

 larvae were found in the branchial cavity of the Grimothea stage of M. gregaria ; this 

 position had evidently only just been assumed, for the larva was still free and no defor- 

 mation of the host had yet occurred. These larval stages are very similar in general 

 appearance to the corresponding stages of P/iryxus abdomi/ialis, Kroyer, as depicted by 

 Sars (1899). 



A striking habit of this parasite is the strong preference shown for the right side of the 

 host. This side was usually the one infected, although infection also occurs on the left 

 side only and on both sides. A consideration of all the hauls between September 193 1 

 and March 1932^^ in which infected specimens were obtained, yields the following data: 



Munida siibriigosa 



Total number examined 

 Number parasitized 

 Parasitized on right side only 

 Parasitized on left side only 

 Parasitized on both sides 



Total number examined 

 Number parasitized 

 Parasitized on right side only 

 Parasitized on left side only 

 Parasitized on both sides 



5798 



429 or 7-4 per cent of the total 

 395 or 92-1 per cent of those parasitized 

 20 or 4-6 per cent of those parasitized 

 14 or 3-3 per cent of those parasitized 



Munida gregaria 



3369 



125 or 37 



114 or 91-2 



10 or 8-0 



I or 0-8 



per cent of the total 

 per cent of those parasitized 

 per cent of those parasitized 

 per cent of those parasitized 



The percentage of parasitization in individual hauls varies from zero to 50 per cent in 

 M. siibnigosa and from zero to 100 per cent in M. gregaria. 



It would seem that an individual of M. siibnigosa infected on the left side has almost 

 equal chances of being infected on the right side as well. This is not so for M. gregaria, in 

 which, of the total of those parasitized on the left side, 90 per cent are infected only on 

 the left side. The asymmetry of Pseudiotie galacanthae mentioned above is evidently 

 impressed by the shape of the cavity of the carapace in which it Uves. Specimens taken 

 from the left side of M. siibnigosa showed an opposite asymmetry to specimens taken 

 from the right, those from the one side giving the appearance of a mirror image of those 

 from the other. This was especially well seen when the parasites from a host infected on 

 both sides were placed together. Thus no reason for the preference of Pseudiotie 

 galacanthae for one side of its host is to be found in its superficial asymmetry. 



One hundred and seventy-one specimens of a large haul of the Grimothea stage of 

 M. gregaria, not included in the above figures, yielded five infected with the Crypto- 

 niscid larva of Pseiidione galacanthae. This represents only 2-9 per cent, a figure rather 

 less than the 37 per cent obtained from the whole season's data. It may be that 

 infection was only taking place at this juncture and that many more Grimothea would 



1 Hauls of the Grimothea stage of M. gregaria are not included. 



