342 
Entozoa of Fishes 
and rapidly begins to macerate after the death of its host. Unless the 
parasite be obtained alive it is extremely difficult to discern the 
outline of the vesicula seminalis externa, and the spines are so minute 
that they might readily escape detection. Otherwise the resemblance 
is so great that there is little doubt Stossich was dealing with the same 
species 1 . The species described by Olsson (1868, p. 36, PI. 4, fig. 83) as 
Distomum increscens is also, as already noted by Odhner (1904, p. 332, 
note 4), in part identical with Distomum bacillare. 
Pharyngora bacillaris (Molin) is the commonest parasite of the 
mackerel and was found at Millport in over 80 °/ 0 . That figure is 
probably above the normal, but it certainly occurs in well over 50 °/o on 
other parts of the coast. It was not met with in any other fish in the 
Firth of Clyde, but elsewhere it is met with frequently in Cyclopterus 
lumpus, Capros aper and not uncommonly in Gadus merlangus. The 
infection is generally in considerable numbers and in Cyclopterus it 
may be enormous. 
All the specimens from Millport were immature or just beginning 
to produce ova, so the following description will be based on specimens 
obtained elsewhere. 
It is a delicate and slender form, generally colourless except for 
the uterus, which has the usual brownish yellow colour. Older 
specimens frequently have a rusty brown colour. The specific name is 
rather apt, for it is elongated and of almost uniform breadth. Dorso- 
ventrally it is considerably flattened. In life its movements are 
comparatively sluggish, resembling in this respect those of Lepidapedon 
rachiaeum, and they are mostly of a forward and backward character. 
It shows less tendency than other Distomes to curl from side to side. 
This may be correlated with the reduction in size of the ventral sucker, 
and may also account for the fact that specimens always die straightened 
out. 
The length of mature individuals is 2—4'5 mm. The maturity size 
appears to lie almost exactly at 2 mm., but an occasional specimen 
without ova was met with over this length. No smaller specimen, 
however, was seen with eggs. The breadth is very uniform. It is 
usually greatest at the level of the testes but there is little difference 
up to the level of the ventral sucker. In front of that it gradually 
narrows to the square-cut anterior end. The posterior end is slightly 
1 From the examination of some of Stossich’s specimens, kindly sent me by Professor 
Monticelli, I have been able to make certain that Stossich was dealing with the same 
species as I am here describing. 
