THE MYXOSPORIDIA OF THE BEAUFORT REGION. 215 



It is very common to find two or more species of Myxosporidia living in the gall 

 or urinary bladders at the same time. This is especially true of the sharks, where it is 

 rare to find an adult whose gall bladder does not contain at least two species. For 

 instance, the gall bladder of a sharp-nosed shark, Scoliodon terrcB-iwvcB, 102 cm. long, 

 taken on August 9, 19 12, contained large numbers of trophozoites and spores of at 

 least four species — Chloromyxum leydigi, Ceratomyxa abbreviata, C. tcenia, and C. 

 sphairophora. 



PATHOGENESIS. 



As a group the Myxosporidia are not particularly injurious. Considering their 

 abundance this is indeed fortunate. Undoubtedly the same factors have been at work 

 here as elsewhere to produce this result. As has often been pointed out, it is to the 

 advantage of the parasite as well as the host to injure the latter as little as possible. 

 Probably the majority of the most injurious species which have arisen have accomplished 

 their own downfall along with that of the host. 



As we would naturally expect, the tissue parasites are much more injurious than the 

 "free" forms. Several of the former are known to be the cause of some of the most 

 destructive diseases of European fresh-water fishes. 



Apparently the "free" parasites for the most part cause but little injury to the 

 host. I/ike so many other protozoan parasites which are common in the cavities of 

 both vertebrates and invertebrates, they seem to have been able to establish relations 

 with the host which admit of the minimum amount of injury. Still, it can hardly be 

 claimed that they are perfectly harmless. Their brief period of intracellular existence 

 must result in the destruction of the epithelial cells in which they develop. In many 

 cases, when specially abundant, they cause the atrophy or hypertrophy of the epithelium 

 lining the cavities in which they develop. Whether they may produce toxic products 

 of any kind which when absorbed by the host may have far-reaching effects we have 

 no certain knowledge. It has been noticed that the bile in gall bladders containing 

 large numbers of parasites is often more watery and has a lighter color than normal, 

 but whether this is of any significance the author is unable to say. Of course, any 

 weakening effects of the parasites on marine fishes would in most cases be difficult to 

 detect. It would, in all probability, simply result in their being quickly captured 

 by some one of their numerous enemies, and the chance of finding fishes which were 

 appreciably weakened would be slight indeed. 



CLASSIFICATION. 



The classification of the Myxosporidia is at present in a very unsatisfactory state. 

 The most common classification is that of Doflein (1899 and 1901). This classification, 

 slightly modified by Auerbach (i 910), is as follows: 



Suborder MYXOSPORIDIA Butschli. 



Legion I. DISPOREA, Doflein. 



Only one pansporoblast, forming two spores, developed in each trophozoite. Trophozoites disin- 

 tegrate after the spores mature. 



Family 1. CERATOMYXID^ Doflein. 



Trophozoites floating freely in various cavities of the host; progressing by amceboid movements. 

 Long diameter of spore at right angles to sutural plane. 



