ENTOZOA — TREMATODA. 
309 
and the reporter, the germ-pouches proceed, in which new Cercaria- 
liie larvsB are developed, by which this chain of metamorphoses, passing 
through several generations, is closed. Of the origin of the Cercaria 
echinata there can be no doubt : they are produced from the Konigsgel- 
ben Wurmern (Eng. king’s-yellow worms), as Bojanus and the reporter 
have observed. These worms, formerly observed by Naturalists as germs 
of the Cercarice, Steenstrup defines as the matrice of the Cercarice and 
Distoma. He is in doubt whether they possess particular openings for 
emitting their brood of Cercarice. However, it seemed to him, that two 
openings were to be found on the constricted band of the matrice of 
Cercaria echinata. The reporter can assure him, that the matrice of 
some species has no definite aperture for emitting their brood, while 
others have a peculiar sphincter behind the opening of the mouth, 
through which they are protruded. Steenstrup has often observed, 
in the winter months, the origin of the young matrice, which the 
reporter was seldom lucky enough to do. In this season were found 
many matrices, which contained nothing but young matrices, in the 
most various stages of development. They developed themselves like 
Cercarice, also out of round granular germs. He farther conjectures, 
that these matrices, which may equally be considered as the first 
matrices of the Cercarice, do not again proceed from matrice-like animals, 
but from the eggs of Distoma ; but, as he could not explain the chain 
of metamorphoses of Cercaria echinata, by direct observation, he left 
it, and appealed to the brood of Monostomum mutahile, which, accord- 
ing to the reporter’s observations, consists of infusoria-like young, 
which all contain a creature very like the matrice of the Cercaria 
echinata. Steenstrup certainly conjectured rightly, that in these 
matrice-like animals, not the larvae of Monostoma but of Cercarice 
were developed, from which afterwards the complete Monostoma pro- 
ceeded ; he also referred this supposition to the Cercaria echinata, in 
order to fill up retrogressively the gap in the series of the metamor- 
phoses of this animal, the transition from the brood of the Distoma to 
the first matrices of the Cercarice. The reporter cannot entirely agree 
with Steenstrup, that the Cercaria echinata is the larva of a Distomum 
accomplishing several metamorphoses, and only wishes that this conjec- 
ture were confirmed by direct observation ; but he cannot help remark- 
ing, that the metamorphoses of the Cercarice to the perfect Distomum, 
could with difficulty take place in the snail itself. The reporter also 
doubts, if the Distoma figured by Steenstrup, without a constricted 
throat (tab. ii. fig. 8 e. and 8 f.), actually belong to the series of metamor- 
phoses of the Cercaria echinata ; he expects at a future period to publish 
his grounds for this doubt in a separate essay ; but the following may be 
here remarked: — If we compare the armed Distoma {Dist. ecMnatum, 
uncinatum, militare, &c.) found in the intestinal canal of water fowls 
353 Z 
