THE MYXOSPORIDIA OF THE BEAUFORT REGION. 213 



intraspecific variation seems to be in size, and many writers have overestimated the 

 importance of this as a specific character. As previously pointed out, there is a marked 

 tendency in many species to form spores rapidly when subjected to unfavorable condi- 

 tions, and such spores are very often undersized and also sometimes show considerable 

 modifications in form. There is evidence that spores from different hosts may show 

 greater differences than those from the same host, but special attention has not been 

 given to this point, which is well worth extended investigation. There is, of course, 

 a possibility that some of the forms described as distinct are simply different strains 

 of the same species developed in different host species. 



OCCURRENCE OF THE MYXOSPORIDIA. 



The more the writer has studied the Myxosporidia the more confident he has become 

 that no group of fishes are free from these parasites. It was only a few years ago that the 

 Pleuronectidse was pointed out as an example of a family which was immune to the 

 attacks of Myxosporidia, but now a number of species are known from fishes of this 

 family. The author has found several species of Myxosporidia in one species of flounder, 

 Paralichthys albiguttus, and it is rare indeed to find a fish that is not infected by one or 

 more of these parasites. The ganoids have also been believed to be free from Myxo- 

 sporidia, but there has been found a species of Sphccrospora abundant in the urinar}' 

 bladder of the gar pike, Lepisosteus platystomus, at Gainesville, Fla. 



Although numbers of species of fishes were examined without finding any evidence of 

 Myxosporidia, it is doubtful if there are many fishes which are absolutely free from these 

 parasites at all times. In most cases the species in which Myxosporidia were not found 

 are those in which only a few fish or only young individuals have been available for exam- 

 ination. Probably the most striking exception is the menhaden, Brevoortia tyrranus, 

 of which large numbers of adults were examined with uniformly negative results. 

 But negative results in such cases are far from conclusive when it is considered that some 

 species of Myxosporidia occur only at certain seasons and at other times no trace of them 

 is to be found. A striking example of this is Ceratomyxa streptospora, new species, which 

 is found in the gall bladder of Chcetodipterus faber. This species was abundant in nearly 

 every fish examined during the early part of June, but no trace of it was found in fish 

 examined during July. 



The occurrence of some species only at certain seasons is probably not a rare phe- 

 nomenon, but to what extent this occurs can only be determined by investigations carried 

 on throughout the ,year. In this connection it is interesting to find that in a number of 

 species only the vegetative forms occur at certain seasons. The best-known example of 

 this is Myxidium lieberkuhni, a parasite in the urinary bladder of the European pike, 

 Esox lucius. Although this species is very abundant, the spores are to be found only in 

 summer, while during the winter the epithelium of the bladder is fairly covered with 

 immense numbers of vegetative trophozoites. The writer has found a number of forms 

 which are not included in this paper, since none but the vegetative trophozoites were 

 discovered, and without the spores it was impossible to determine with certainty the 

 genera to which they belong. In a number of other instances the vegetative trophozoites 

 were very abundant, occurring in a large proportion of the fish examined, and yet the 

 spores were so rare that they were found only after a long and arduous search. In the 

 case of some species practically all stages in the development of the trophozoites can be 



