THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 99 



infection of epithelium. Tlie typical myxosporidian spore-form is 

 accordingly not of siicli preeminent importance. Further : 



Whether the differentiation of the Sporidia, heretofore principally based upon the 

 structure of the spore, will permit itself to be maintained is a matter for zoologists. 

 The following investigations show too often how little stress is to be laid upon this 

 mark alone, and what variations occur through adaptation. 



Compared with the Gregarines, the Myxosporidia show their lower 

 position by the lack of constant body form. 



In the second edition of the same work (1891, pp. 7, 8, 10) he reduces 

 his family Sporidia to the rank of a subfamily of the fiimily Coccidia. 

 He regards the "psorosperm" as a resting spore, and says it may be 

 the equivalent of the individual falciform germs of the Sarcosporidia. 

 The capsules, lie says, also occur in the sarcosporidian spore (see p. 88). 



The following is, I think, a fair summary of the evidence : 



The Myxosporidia differ from the remaining Sporozoa in the multi- 

 nucleate amoebiform adult, the pansporoblastic spore formation, ^d 

 especially in the capsulate spores, which never contain falciform germs. 

 At the same time the consensus, and I believe the evidence, favors 

 their retention in the Sporozoa^ of which they form a rather aberrant 

 subclass. 



As regards the relation of the Myxosporidia to the Myxomycetes is 

 there any evidence that the myxosporidium is a plasmode? In the 

 diagnosis of the myxomycete plasmode the following are the most 

 important points : 



(a) Actual observation of plasmode formation by fusion of individuals. 

 Now, not only has this never been seen^ in the Myxosporidia, but the 

 multiple nuclei of the myxosporidium are knoAvn in several cases to 

 (and in all probability always do) originate by the division of the primi- 

 tive single one. 



(b) The presence of various shades of red, brown, or black pigment. 

 This has never been seen in the Myxosporidia. All pigment there found 

 appears to be of extraneous origin.^ 



Add to this the differences in the methods of spore formation (and 

 particularly the fact that spore formation in the Myxosporidia does not 

 terminate the life cycle) and the further fact that, asBiitschli remarks 

 no known myxomycete spore has any structure comparable to the 



' Of course it may hereafter be found, but it will be time enough to approximate 

 the two groups when it is found. 



Even if its existence were demonstrated (and, from sarcosporidian analogy, Pfeiffer 

 regards it only as probable), the process described by Pfeiffer (Die Protozoen als 

 Krankheitserreger, 1 ed., 1890, p. 34; 2 ed., 1891, p. 108; see also p. 227) in the 

 muscles of the barbel could not possibly bear this construction, as the myxosporidium 

 fusion here described is not zoologic, but secondary to common incapsulation, and 

 is rather comparable to fusion of abscesses and ovarian cysts, where the adjacent 

 walls disappear from pressure-atrophy, or otherwise. 



This fusion process under pressure has also recently been observed by Korotneflf 

 (see p. 188). 



* This statement must perhaps now be liualitied; see pp. 77,277, 



