452 WILLIAM NICOLL. 
prominence of the ventral sucker and the conspicuousness of 
the yolk-ducts were features unfamiliar to me im my previous 
experience of the species. As a matter of fact, however, 
they are due to the method (in fresh water) which Johnstone 
employed in killing his specimens. I have since found Podo- 
cotyle atomon in various species of fish, and tried the ex- 
periment of killing some in fresh water, in which they assumed 
the same shape and appearance as Johnstone’s specimens. 
One of the most striking features of Johnstone’s specimens 
was the distinctness not only of the yolk-ducts but also of 
the yolk-glands themselves. On that account their disposi- 
tion could be easily observed, and this is shown very well in 
Johnstone’s figure. One point to which he makes no refe- 
rence is the occurrence, in about every third specimen, of an 
asymmetrical group of follicles in front of the ventral sucker 
on the right side. This had not the linear arrangement of 
the other follicles, but was more dendritic, and from it a 
separate duct passed down to join the longitudinal duet. 
This asymmetrical group was never observed on the left side. 
I have since collected a number of specimens showing the 
same characteristic but differing in no other respect from 
Podocotyle atomon. It seems to indicate what might be 
regarded as a distinct variety, and for this I propose the 
provisional name P. atomon var. dispar. 
During a recent visit to the Firth of Clyde, I have obtamed 
Podocotyle atomon from numerous species of fish, Gadus 
virens, G. pollachius, Pleuronectes flesus, Pl. 
platessa, Cottusscorpius, C.bubalis and Centronotus 
gunnellus, and have been struck with the remarkable 
diversity of form which it presents. It displays variation in 
the extent of the yolk-glands, the length of the cirrus-pouch, 
the shape and situation of the testes, and, in particular, the 
size of the ova. I have to add Gastrea spinachia 
(fifteen-spined stickleback) as an additional host on the east 
coast, and in the specimens from this host the ova were 
exceptionally large, reaching a length of nearly ‘1 mm. This 
Trematode, if all the specimens be really identical, is very 
