A PARASITE OF THE PIKE 245 



sites of the tope, shark, and the various wrasses being 

 deleterious to the hosts. 



The Polysporea are much more important economi- 

 cally than are the Disporea. This is not surprising, 

 for the faculty of producing numbers of spores 

 instead of two only gives increased chances of 

 transferring the infection from host to host. It also 

 ensures the perpetuation of the species to a much 

 greater extent than when two spores represent the 

 limit of the reproductive capacity of the trophozoite. 

 The power of inflicting damage upon their hosts 

 seems more intense among the Polysporea than 

 among the Disporea. Their power of movement is 

 greater, their pseudopodia frequently seem more 

 abundant, and many have a purely vegetative method 

 of multiplication in addition to spore formation. A 

 large species of Myxidium is a common parasite of 

 the urinary bladder of the pike. Its spore formation 

 occurs during very cold weather, and it is not com- 

 monly seen in England. But an infected pike can 

 be recognized almost at once, for its urinary bladder 

 is flecked and streaked with yellow patches, which 

 show through the thin-walled organ. These flecks 

 may become so numerous in later stages of the in- 

 fection that they show as a continuous slimy layer 

 over the entire inner surface of the bladder. This 

 slimy layer consists of innumerable trophozoites of 

 Myxidium lieberkuhni. These trophozoites bud in a 

 remarkable fashion, and the general protoplasm 

 contains a large number of nuclei, some of which 

 pass direct into each bud. The buds gradually 

 become separated and pass away as new small 



