312 
REPORT ON ZOOLOGY, MDCCCXLII : 
with small round or oval bodies ; these are the germs of Distomum du~ 
plicatum, Baer, which Steenstrup could not observe becoming pupa. 
He adds to these observations, that the tailed Distom. duplicatum is 
very probably the larva of Aspidogaster conchicola, Baer. The 
reporter considers this conjecture as entirely groundless; the tailed 
Distom. duplicatum can only change into a Distomum. It possesses, 
like all of them, a forked intestinal canal, and an abdominal acetabulum. 
Aspidogaster has not an abdominal acetabulum, and is only furnished 
with a simple intestinal pouch. The brood also of Aspidogaster, which 
the reporter has frequently observed, does not at all agree in form with 
those creatures of the Paramecium-\md from which Steenstrup asserts 
that the matrice for Distom. duplicatum proceed. Its young are pro- 
vided with a distinct acetabulum of the mouth, under which the anterior 
end of the body projects like a moveable tongue, and already points to 
the shield-formed abdominal plate of the grown animal. Steenstrup 
correctly explains, in opposition to the assumption of Cams, that the 
pouch-like beings, which have been named Leucochloridium paradoxum, 
proceed, by equivocal generation, from the parenchyma of the Succinea 
amphibia; that these pouches are the nurses of certain Trematoda, 
and, in his opinion, owe their origin to ciliated animalcules, resembling 
the Opalina ranorum. 
Steenstrup found, in the eyes of fishes, Trematoda, not only free but 
shrivelled up, which were fixed to the inner wall of the cornea of a pike 
(Hechtes) and of a perch (Barsches), and to which a fine granular unorga- 
nized stripe ran through from the external surface, which might be looked 
upon as the way by which the Trematoda-\^e little animal got from the 
outside into the fish. As he also found such Trematoda become pupa in 
the neighbourhood of the eyes of fishes, he looks upon this to be a proof, 
that the Diplostoma, Holostoma, and Distoma, living as parasites in their 
eyes, are different links of one series of metamorphoses. He explains the 
Diplostomum clavatum to be the larva, Holostomum cuticola the pupa, 
and Diplostomum volvens the full grown Trematodum of one and the 
same series of metamorphoses ; with which the reporter does not agree, as 
these three Trematoda are formed differently from each other, and no 
trace of sexual organs can be recognised in the Diplostomum volvens. 
Whether the Trematodum found enclosed, in the state of pupa, under 
the cuticle and in the mesentery of the Rana temporaria, be the pupa 
of Amphistomum clavatum, as he imagines, would need more proof. The 
reporter has often found the same sort of capsuled Trematoda in frogs ; 
but he always held them for Distoma without sex, never for Amphistoma. 
A laboured article by Streubel, on the genus Pentastomum, in Ersch 
and Gruber’s “ Encyclopa 0 die 16r Theil. 1842, p. 93,” which has hitherto 
contained distinguished original essays on the Helminthes, is almost only 
a meagre extract from Diesing’s Monegraph of this genus. 
A very singular parasitical worm, which the reporter knows not 
356 
