SEA-FISHERIES LABORATORY. 131 



different from the true cysts in Johnstone's plaice, which 

 I will call in future specimen A. Before describing the 

 two varieties minutely, it will, perhaps, help to understand 

 their structure, to give briefly the course that the develop- 

 ment of the parasites has followed in the two cases. 



In both, the infection is a ripe, well-matured one, but 

 whereas in A it is very strong, and must have proceeded 

 from a great number of centres (in other words, the host 

 swallowed very many spores), in my plaice (B) it is only 

 a slight one. Perhaps this supplies, at any rate partly, 

 the reason for the fact that here the individual parasites 

 have tended to spread the infection further, invading the 

 neighbouring tissue of the host largely by the process of 

 endogenous multiplication (" multiplicative reproduction " 

 of Doflein (1)) in the young forms. Indeed in the case of 

 Glugea, where cell-infection prevails, this condition of 

 diffuse infiltration is, to a very considerable extent, the 

 result of endogenous reproduction, and, therefore, ap- 

 parently differs rather in origin from the condition 

 as it is generally understood to occur in the larger Myxo- 

 sporidia ; although I think it is by no means unlikely that, in 

 these also, it will be found that endogenous reproduction 

 has a larger share in the result that is at present ascribed 

 to it, for Doflein (I.e.) describes in one instance (Myxdbolus 

 cyprini, the cause of " Pockenkrankheit ") a similar multi- 

 plicative reproduction of young forms while still intra- 

 cellular. There is, therefore, no need to restrict, as he 

 would, the term diffuse infiltration to such larger forms, 

 which, when adult, are intercellular. Thelohan, in first 

 describing the condition, was not aware of this endogenous 

 reproductive capacity, and looked upon it as a more or less 

 continuous ramifying infiltration of the parasitic body, 

 with displacement and disturbance of the surrounding 

 tissue. Whereas, as we have just seen, it is far more 



