408 Geoflfrcy Sniitli 



inachi, the body cavity was also full of liberateci sporozoites, the 

 haemolymph having a milky appearance due to the crowded pre- 

 seuce of these bodies. The testes were in all cases disinteg-rated, 

 only the vesiculae seminales remaining. Unmodified males were 

 also fouud to contai)! the cysts of Aggregata inachi, but in none of 

 these males were there large quantities of sporozoites in the haemo- 

 lymph, so that it appears that the hermaphrddite externa! charaeters 

 are assumed by the iufected male at the moult Avhieh follows the 

 liberation of a large quantity of sporozoites. 



It is impossible to prove from the instanees hefore us that the 

 presence of the parasite is the cause of the castration, but that 

 this is the case is certain from the analogy of other instanees, 

 a detailed analysis of which I hope to furuish in a forthcoming Avork 

 on the Rhixocephala. 



With regard to the effect of this parasite on the female I am 

 unable to furuish any facts, owing to the rarity of the female in 

 general. 



2. Life history of Aggregata inaclii. 



It will be remembered that the Aggregatidae together Avith the 

 Porosporidae form a separate sub-tribe Gymnosporea, distinguished 

 from all other Gregarines by the faet that the ripe eyst contains 

 naked sporozoites AAhich are not invested in special sporoeysts but 

 are irregularly grouped round residual masses of nutritive matter. 

 The mature cysts of the Gymnosporea thus come to have an extra- 

 ordinary resemblance to the cysts of the Malarial parasite found in 

 the Mosquito. This resemblance is brought out in Fig. 12, Piate 26. 



In the adult trophozoite stage, hoAvever, the Gymnosporea are 

 typical septate Gregariues, as there seems to be no doubt that ob- 

 servers are correct Avho associate the septate Gregarincs fouud in 

 tbe gut of the Crustacea Avith the coelomic cysts situated on the 

 outer surface of the gut in the body cavity. 



The life history of these Gregariues is exceedingly obscure: 

 nothing is knoAvn of the means of infection or Avhether the sporo- 

 zoites are taken up by an intermediate host before infecting another 

 crab, though tiiis appears highly })robable from the observations of 

 Frenzel(3; that the parasite« seem to be absent from the crabs at 

 certain times of the year. 



The question to the solution of Avhich I AAish to contribute some 

 fairly definite evidence relates to the occurrence or non-occurrence 



