94. CLAPAREDE, ON TREMATODA, ETC. 
chyma of the animal, would appear to represent the first 
stage of a process of calcification. They are regarded by 
him therefore as a pathological product; but I see no reason 
for looking upon them in any other light than as being alto- 
gether normal. 
Upon my communicating, a short time since, to Dr. G. 
Wagener, my observations on the calcareous corpuscles of 
the Diplostomata, he told me that he had been long acquainted 
with their relation to the excretory system, but that he had 
not made it known; showing me also some drawings of the 
appearances he had observed. At the same time he en- 
couraged me to investigate other species. The first subjects 
which suggested themselves were the immature forms of 
Holostoma, the Diplostomata themselves being manifestly 
nothing more than Holostomatous larve. Steenstrup had 
already pointed out the relationship between the Holostomata 
and the Diplostomata, and propounded the view that Diplo- 
stomum clavatum, Holostomum cuticola, and Diplostomum 
volvens are one and the same species, of which the two 
former would represent the immature, and the latter the 
mature animal. But this association appears to be the less 
maintainable since Diplostomum volvens is as much an im- 
mature form as Diplostomum clavatum. Nevertheless, it is 
indubitable that the mature forms of these various ani- 
mals must belong to the genus WHolostomum. Several 
immature Holostomata are, as is well known, characterised 
by a network composed of calcareous corpuscles disposed in 
regular order in the integument, as for instance Holostomum 
cuticola. As the latter species was not at the moment ob- 
tainable, I directed my attention in the first stance to some 
Trematode-cysts from the peritoneum of the Stone-Perch 
(Acerina cernua). The cysts, of an oval form, were about 
0°50—O0°60 mm. in length, and easily lacerable. The animal 
contained in them, presented in many respects an unmistake- 
able resemblance to the Holostomum-type, though differing 
considerably in several points. The excretory system con- 
sisted of two principal trunks running down each side of the 
body, and opening into a double contractile vesicle, closely 
resembling that of Diplostomum volvens. These lateral 
trunks were of extraordinary dimensions ; so that the internal 
organs were separated by a wide interspace from the wall of 
the abdomen; they presented a chambered or moniliform 
appearance, owing to the circumstance that numerous bands 
proceeded from the external wall of the body to the internal 
organs, and served to retain them in their situation. The 
lateral trunks were filled with minute calcareous particles. 
