Fig. 73.—Sac with psorospermiæ, in the Sepia officinalis.
The Asellus aquaticus seems also to serve as the vehicle of the Echinorhynchus angustatus. The hooks of the embryos differ from those of the adults, as the six hooks of the cestodes differ from the crown of the adults. Leuckart has described those of the envelope of the Echinorhynchus proteus and the Echinorhynchus angustatus. The embryo of the Echinorhynchus has only two large hooks on each side, but several smaller ones. The two species mentioned above have on each side five or six hooks placed at right angles with the median line, but they are not all of the same size.
The animals are allied to the Gordii in their development. In fact, their development is like that of the echinodermata; the larva is the Pluteus, in which the true echinorhynchus develops itself, borrowing the skin of the pluteus. According to the experiments made by Schneider, the larvæ of cockchafers must be the vehicles of the
Echinorhynchus gigas. Pigs disseminate the eggs, and the embryos infest these larvæ, in the bodies of which they pass through their principal changes.
The Gregarinæ are microscopic beings, with an extremely simple organization, the nature and the genealogy of which have only lately been known. They live at first encysted by thousands together, under the name of Psorospermiæ; they are afterwards hatched in the form of Amœbæ, and then transformed into Gregarinæ. They migrate from one animal to another, or from one organ to another, to settle in the intestine, where they assume their adult form. In this state they are monocellular, and do not at any time possess organs which resemble the sexual organs of other classes. The disease of silk worms, known by the name of “pebrine,” has been attributed to the development of psorospermiæ.
We give the representation ([Fig. 74]) of gregarinæ which we have found abundantly on the Nemertes; and ([Fig. 75]) a peculiar species which lives in the larva of an agrion.
Fig. 74.—Gregarinæ of Nemertes Gesseriensis.