STUDIES ON THE DIGENETIC TREMATODES. 479 
‘15 mm. and ‘19 by ‘15 mm. respectively. The ovary is also 
smaller—115 by °105 mm. The uterus is more voluminous 
behind the posterior testis and overlaps the testes to a slight 
extent. The ova are brownish-yellow and measure *0308 
by °0193—0212 mm. The length is practically invariable, but 
one abnormally large ovum was observed in the posterior loop 
of the uterus, measuring ‘0327 by 0212 mm. The average size 
may be taken as ‘031 by ‘021 mm. ‘They are not truly ellip- 
soidal, there being a slight flattening on one side, which pro- 
bably accounts for the variation in the breadth. The shell hasa 
thickness of ‘0008 mm. The vagina lies on the right side of the 
ventral sucker and extends as far back as its posterior border. 
It is marked off from the uterus by a distinct constriction. 
lts diameter is ‘015 mm. and its walls are ‘(006 mm. thick. 
The yolk-glands are less voluminous than in the first 
specimen. ‘They are entirely lateral and extend only a short 
distance in front of the ventral sucker. This might be 
ascribed to imperfect development, but as both specimens 
were fully mature it seems more reasonable to allow that 
some variation may occur in the extent of the yolk-glands. 
In this respect Braun,' in discussing the distinction between 
Pl. elegans (R.) and Pl. cirratus (R.), remarks that much 
weight cannot be placed on the relative extent of the yolk- 
glands, for they vary even in examples from the same host. 
This specimen differs from the first mainly in the condition 
of the vesicula seminalis, the extent of the yolk-glands, and 
the size of the genital glands. Until more material is avail- 
able it is impossible to say whether these features are of 
specific importance or merely variations. 
The species which follow are introduced mainly for the 
purpose of presenting figures which were omitted from a 
previous paper.” Little opportunity has offered of making 
1“ Fascioliden der Vogel.,” in ‘ Zool. Jahrb.,’ syst. xvi, pp. 37-55, pl. 
iii, figs. 25-34a. 
?“ Observations on the Trematode Parasites of British Birds,” in 
* Annals and Mag. Nat. Hist.’ (7), xx (1907), pp. 245-271 
