THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 207 



have all asserted this couditioa. It is, however, almost impossible for 

 me to believe that a tailed species is ever (except of course from break- 

 age, and I have seen many spores deceptively broken) iintailed or that 

 an Iintailed species is ever tailed. I do not recognize as true tails those 

 l)rocesses evidently monstrous (as shown by their aspect, their great 

 rarity, their wide divergence from the tyjiical forms, and the lack of 

 transitions thereto) which are very rarely observed in untailed species. 

 Thus I have seen among hundreds of spores of Myxoholus ohlongus 

 such a form. But that (and also those reported by others belong, I 

 suspect, to the same category) should not be confounded with a true 

 tail. In other words, I believe the j)resence or the absence of a tail to 

 be a good specific character, but not a generic one. Finally, even if the 

 above observations should be admitted to be accurate, might not the 

 conjunction be better exijlained on the supposition that the 2 forms 

 were in the same tumor, but not necessarily (at least until i)roven) in 

 the same cyst, i. e., produced by the same myxosporidium. Although 

 such a close apiDrosimation of 2 different species in the same tumor has 

 not been seen, Th^lohan is authority for an equally close api)roxima- 

 tion of 2 different genera in the renal tubules of Gasterosteus aculeatus 

 and those of Pygostcus imngitiiis. Finally, in this connection pp. 245, 246 

 should be consulted. I saw Weltner's res'ults long after writing the 

 above, and perhaps they may demand some modification of it. 



Shell. — This structure is bivalve throughout the whole of the genus, 

 the valves being superior and inferior. 



Ribhons ("elastic ribbons" of Balbiani). — These curious and prob- 

 ably abnormal modifications of the ridge are found only in, and are 

 described under, Myxoholus ellixisoides (j). 223). 



Tail (see also pp. 245, 250, 254).— Tliis structure is found only in some 

 species of Myxoholus. It was first noted by Mliller, who says ' that it 

 is merely a solid prolongation of the shell substance not containing any 

 extension of the body cavity. This is also, I believe, the view of its 

 structure entertained by all subsequent observers. 



Balbiani regards the tail as formed by the coaptation along the 

 median line of his "elastic ribbons" (p. 223). The tail would thus 

 consist of 2 lateral halves. This view may be safely rejected, as, if the 

 tail is really composed of two halves, the latter must be superior 

 and inferior, and not right and left. The latter view of its structure 

 (2 halves, superior and inferior) is taken by Th^lohau,^ who says that 

 the tail is composed of 2 halves (the respective superior and inferior 

 positions of which are necessarily implied, since he says the bifurcation 

 always takes ijlace in the longitudinal plane), whose occasional imper- 

 fect coaptation results in the bifurcate condition frequently observed. 



Finally, since writing the above, I have been enabled, by the kind- 

 ness of Prof Beth E. Meek, to examine Myxoholus of. linearis (p. 253), in 



1 Miiller's Archiv., 1841, p.. 479. 

 «Aunal. de Microgr., 1890, ii, p. 206. 



