W. Nicoll 
325 
which occurred in nearly a quarter of all the fishes. It was especially 
frequent in the gadoid fishes, to the extent of nearly 40 °/„. Next to 
Podocotyle atomon, Zoogonoides viviparus and Ascaris clavata were the 
commonest parasites, each occurring in over 16 °/o> the former especially 
in the Pleuronectidae (61 °/ 0 ) the latter in the Gadidae (65 %)• 
Altogether 22 species of Trematodes were obtained. This compares 
favourably with St Andrews where over a much longer period only 25 
species were met with; and with the Northumbrian coast where Miss 
Lebour (1908) has determined the presence of 22 species of digenetic 
Trematodes. From these three localities a total of 40 species has now 
been recorded. 
SYSTEMATIC SECTION. 
TREMATODES. 
Sub-family I. Allocreadiinae Looss 1899. 
Next to Allocreadium Looss sens, str., Peracreadium Nicoll 1909 
appears to be the most typical genus of this sub-family. It diverges 
from the fundamental type in the enormous development of the cirrus- 
pouch and in the extensive distribution of the yolk-glands. It resembles 
Allocreadium in almost every other particular. The main lines along 
which, in the sub-family, variations from the type proceed, are in 
the direction of (1) the displacement of the genital aperture; (2) the 
lengthening or shortening of the cirrus-pouch ; (3) the lobing of the 
ovary; (4) the more extensive distribution of the yolk-glands and (5) 
the growth of filaments on the ova. 
In the first direction Podocotyle (Duj.) Odhn. 1904 represents the 
extreme and it also presents a transition stage in respect of the ovary, 
cirrus-pouch and occasionally of the yolk-glands. The position of the 
genital apertui'e distinguishes the genus from all the other genera but 
in Lebouria Nicoll 1909 we have a well-defined intermediate stage in 
which the displacement has proceeded only a very short distance. 
There is not wanting evidence, moreover, in several as yet imperfectly 
known species to indicate that more intermediate forms exist. With 
regard to the cirrus-pouch Allocreadium, Helicometra Odhn. 1902 and 
Lebouria represent the typical short, plump form, although in the last 
named there has entered a modification of the pars prostatica which is 
met with again in Podocotyle. This genus and Cainocreadium Nicoll 
1909 are the intermediate stages towards the extreme development in 
Peracreadium. The typical form of the ovary must be regarded as 
Parasitology ni 
21 
