THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 207 
have all asserted this condition. 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) untailed or that 
an untailed species is ever tailed. I do not recognize as true tails those 
processes evidently monstrous (as shown by their aspect, their great 
rarity, their wide divergence from the typical forms, and the lack of 
transitions thereto) which are very rarely observed in untailed species. 
Thus I have seen among hundreds of spores of Myzxobolus oblongus 
such aform. 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 presence 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 explained on the supposition that the 2 forms 
were in the same tumor, but not necessarily (at least until proven) in 
the same cyst, i. e., produced by the same myxosporidium. Although 
such a close approximation of 2 different species in the same tumor has 
not been seen, Thélohan is authority for an equally close approxima- 
tion of 2 different genera in the renal tubules of Gasterosteus aculeatus 
and those of Pygostcus pungitius. Finally, in this connection pp. 245, 246 
should be consulted. I saw Weltner’s results 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. 
Ribbons (‘elastic ribbons” of Balbiani).—These curious and prob- 
ably abnormal modifications of the ridge are found only in, and are 
described under, Myxobolus ellipsoides (p. 223). 
Tail (see also pp. 245, 250, 254).—This structure is found only in some 
species of Myxobolus. It was first noted by Miiller, who says! that it 
is merely asolid 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 Thélohan,? 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 place in the longitudinal plane), whose occasional imper- 
fect coaptation results in the bifurcate condition frequently observed. 
Finally, since writing the above, f have been enabled, by the kind- 
ness of Prof. Seth H. Meck, to examine Myzobolus ef. linearis (p. 253), in 
1 Miiller’s Archiv., 1841, p. 479. 
* Annal. de Microgr., 1890, 11, p. 206, 
