104 
Diseases of Fish 
On teazing out portions of the pigmented areas, minute spherical 
vesicles, and the ‘yellow bodies’ so often associated with infections by 
Myxosporidia, were visible under the microscope. Sections showed 
that the muscular tissues in the centre of the lesions were much 
degenerated. The muscle fibrils were partially, or in places completely, 
replaced by a finely granular material contained within the sarcolemma: 
the shape of the fibrils was seldom altered, but the sarcous elements 
within the sheath were usually destroyed. 
In the regions surrounding the areas of most acute infection some 
inflammation was present, and the interfibrillar spaces contained many 
leucocytes: the striation of the muscle was also somewhat less pro¬ 
nounced than in the normal tissue. The ‘yellow bodies’ were plentiful 
in the centre of the lesions. 
Small spherical vesicles, averaging about 30 p in diameter, were 
present in the interfibrillar tissue, or actually within the fibrils. Each 
vesicle was bounded by a thin structureless transparent membrane, 
resistant to potassium hydrate solution. Each contained a mass of 
protoplasm showing stages of division into a large number of spores 
(more than 8). These vesicles appear to resemble the condition 
described by Gurley as occurring in Pleistophora typicalis (found in the 
muscles of Gottus Scorpio), in which the pansporoblast membrane is 
sub-persistent as a polysporophorous vesicle which represents the 
pansporoblast stage. 
The spores were oval in shape, about 3 p long, and 2'5 p broad ; they 
contained a small granular area, staining with haematoxylin and basic 
dyes, which probably represents the nucleus. No polar capsules could 
be seen, but this was possibly due to the imperfect preservation of the 
specimen. 
As in the case of Pleistophora typicalis, the trophozoite stage was 
not observed. Some small protoplasmic masses, containing several 
definite nuclei, were found within the fibrils and in the interfibrillar 
tissue and these probably represent stages in the formation of the 
pansporoblast. Adopting Minchin’s classification, it would appear that 
this parasite belongs to the 
Order 
Myxosporidia (Biitschli) 
Suborder 
Gryptocystes (Gurley) 
Family 
Glugeidae (Theloran) 
Section 
Oligosporogenea (Doflein) 
Genus 
Pleistophora (Gurley) 
Species 
? Nov. 
