346 Records of the Indian Museum. [Vol. X\, 



are for the spore membrane. Thus the transformation into the adult 

 spore is brought about (figs. 24-25). 



Structure of the spore. — A fully formed spore is an elongated pear- 

 shaped body, rounded at the posterior extremity and acutely pointed 

 anteriorly (fig. 26). It is symmetrical bilaterally, but not antero- 

 posteriorly. The size of the spore varies from 30 to 32 fx in length, 

 and from 7 to 8 jui in breadth. The spore-wall is formed of two valves ; 

 the point of junction of these valves is distinctly thickened, and can be 

 seen, in a side view, as a slightly raised ridge. The ridge lies parallel 

 to the long axis of the spore. Only one }iolar capsule is present in each 

 spore. It is of a large size, 22 to 23 jx in length, and has the same shape 

 as the parent spore. In the polar capsule a much coiled thread can be 

 easily seen, as also the opening of the duct for the extrusion of the 

 thread or polar filament at the anterior pointed extremity of the capsule 

 and the spore (fig. 27). The length of the polar filament, in the spores 

 measured, varied from 92 to 97 fJt. The nucleus of the capsulogenous 

 cell is seen lying at the periphery of the polar capsule, on one side, near 

 the posterior extremity, as an elongated body. In the protoplasm 

 of the spore itself an iodinophilous vacuole, 3 '6 jx in diameter, is pre- 

 sent. Lying just posterior to it is the nucleus of the spore. A few 

 granules of chromatin were also seen lying scattered in the proto- 

 plasm. 



Systematic position. — From the preceding description it will be 

 clear that our form is a Myxosporidian. Following Labbe's classifica- 

 tion it falls in the Family Myxobolidae, and the genus Myxoholus, 

 Butschli, in having bilateral symmetry and a bi-valve shell, with the 

 valve junction plane parallel to the long axis of the spore, and further 

 in having an iodinophilous vacuole in the protoplasm of the spore, and a 

 single polar capsule at the anterior end. 



The species of this genus are grouped under two heads, viz., one with 

 a single and the other with two polar capsules. So far, only five uni- 

 capsulate species of the genus Myxobolus have been recorded. These 

 are : — 



M. piriformis, Thelohan. 

 M. unicapsulatus, Gurley. 

 M. fufirmanni, Auerbach. 

 M. ocuU-leucisci, Trojan. 

 M. toyamai, Kudo. 



Our form, like M. piriformis and M. toyamai, occurs on the branchiae, 

 and differs in this respect from the other three unicapsulate forms. Com- 

 pared with all the previously described unicapsulate forms our species 

 is a very large one. Tlie size of the cyst, the spore, and the polar cap- 

 sule is much larger than in any of the other forms, and these are the 

 characters on which the classification is chiefly based. The shape of 

 the spore slightly resembles that of M. toyamai, though the anterior 

 extremity of the spore, instead of being attenuated, is sharply pointed. 

 Calabash-shaped spores, recorded from M. toyamai, are not present in 

 our species. For, these reasons we consider the present form to be a 

 new one, and have called it Myxoholus rohitae after the name of the host. 



Habitat. — The gills of Laheo rohita (Ham. Buch). 



