STUDIES ON THE DIGENETIC TREMATODES. 415 
must therefore be capable of considerable dilatation It is 
surrounded by lax connective tissue, in which are embedded 
the peri-vaginal cells already referred to. 
The ova are usually less than 100 in number. ‘The shape 
is ovoid, slightly blunter at the opercular pole. The shell is 
‘0018 mm. thick and bright yellow, not darkening much 
throughout the uterus. ‘he size of the ova is ‘075-080 by 
040-044 mm.; this is somewhat larger than the size quoted 
by Olsson, but agrees closely with that of Linton. ‘There is 
absolutely no intra-uterine segmentation, the ovarian ovum 
remaining undivided till deposition. The yolk-cells within 
the egg also remain unchanged, and can be easily distin- 
guished from the ovarian cell by their bright red nuclei, the 
nucleus of the ovarian cell taking on a darker, nearly purple 
colour with hemalum-eosin. 
Olsson’s figure (Pl. IV, fig. 52) gives a somewhat erroneous 
impression of the appearance of the ova and uterus in a 
specimen of average size. The ova are usually propor- 
tionately larger and the convolutions of the uterus are 
indistinguishable.! 
Systematic position of Distomum laureatum Zeder. 
The inclusion of this species within the sub-genus Crosso- 
dera by Dujardin in 1845 need not be discussed here. ‘The 
most recent attempt to define its systematic position is that 
by Braun,? and his classification is accepted by Looss,”® 
Heymann,‘ Pratt? and Stafford®. Braun included it in a new 
genus, Crepidostomun, of which the type is C. metcecus 
(Brn.) from bats. The two species are certainly very nearly 
‘In the two specimens from Olsson’s collection which I examined 
the uterus does not have the disposition represented by Olsson. The 
ova are congregated more over the dorsal surface of the ventral sucker, 
so that they are best seen on viewing the animal from the dorsal surface. 
** Annal Hofmuseum, Wien,’ xv (1900), p. 282. 
3* Zool. Jahrb. Abth. Syst.,’ xvi (1902), p. 453. 
**Thid.,’ xxii (1905), p. 97. 
°* American Naturalist,’ xxxvi, p. 957. 
§ * Zool. Anzeiger, xxvii, p. 490. 
