THE MYXOSPORIDIA, OR PSOROSPERMS OP FISHES. 245 



one from which the ''tails" proceed) as the posterior. Zschokke, how- 

 ever, states that he has often seen a fine canal running from the (on 

 the above supposition) posterior end of each capsule to the base of the 

 " tail," and expresses his belief that, in this species as in those observed 

 by Balbiaui, the function of the "vesicles" is to contain the "tails." 

 Both he and, subsequently, Linton' perceived the anomaly which, upou 

 his view, is presented by this species, but neither of them discusses it at 

 length. It is almost as difficult to reverse the position of the spore and 

 consider the " tails" as corresponding to the filaments which in other 

 species are extruded from the capsules, as this view would necessitate 

 the admissions that the capsules are placed at and converge toward 

 the posterior end of the body, and tliat the filaments are extruded from 

 their posterior ends, a state of things occurring in no other known 

 species.^ I may add that the filiform aspect of the so-called " tails " is 

 quite diflerent from that shown by the stout tails of other species, 

 while it closely resembles that of the capsular filaments. 

 69. Myxobolus cf. crepliiii. PI. 30. 



Myxosporidian spore of £sox htciiis, Weltner, 1892, Sitziings-Ber. Ges. Naturf. 

 Freuude Berlin, 1892, pp. 28-36, figs. 1-16. 



The fish was a spawner, weight estimated at 1 kilo; it showed a mass 

 of milk-white eggs whose contents consisted of myxosporidian sjiores, 

 a granular mass, and a few yolk granules. The material was first exam- 

 ined by Hilgeudorf, who recognized the myxosporidian spores. 



Spore dimorphous, untailed and tailed forms occurring. Anterior 

 end more or less bluntly rounded. Posterior end showing great differ- 

 ences, as a rule gradually drawn out without any boundary into the 

 thin tail. More rarely the alternation is sudden and the tail is then 

 delimited from the body. With some spores there is found at the 

 place of transition of the body into the tail a wing-like expansion, 

 which lies at the border of the spore. The untailed spores have the 

 posterior end rounded, much blunter than the anterior ; otherwise they 

 are formed entirely like the tailed. The tailed spores are of a fasiform 

 shape. 



Eelation of untailed to tailed : It might readily be believed that the 

 tailed develop from the untailed by the appearance of a short stump, 

 which would subsequently grow in length and breadth; thus the body- 

 length of the 2 forms is about the same, the whole length of the tailed 

 consequently exceeding that of the untailed only by the length of the 

 tail. Also the maximum width is about the same for both spore-forms. 



Shell consisting of 2 thick almost always unequally arched^ valves 

 which can gape apart anteriorly for more than half their length ; by 



'Bull. U. S. Fish Com. for 1889 (1891), p. 101. 



^M. diplurus has (if Biitschli's figure be correct, pi. 36, fig. 4) the capsules poste- 

 riorly placed, but their convergence and divergence is not evident, and nothing is 

 known about the capsular filaments. 



3 Weltner refers to his figs. 8 to 11, in which the inequality of valve-convexity 

 might perhaps be the result of the oblique positions of the spores. 



