: Animal Parasites and Messmates by Beneden P J Van Pierre Joseph - Parasites

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er may be born before her mother, and even before her grandmother.

We are now about to study some of these mysterious travellers which have given so much trouble to naturalists to discover their abode 197 and determine their identity. Considering the number of observers who have mentioned these distomes, it is evident that these parasites must be very common. We find the names of Ruysch, Leeuwenhoek, Swammerdam, Camper, Houttuyn, Mulder, Heide, Biddloo, Snellen, etc., among the naturalists who have made them a subject of study. In our own day, the writers who have explored this territory are so numerous that we should require more than a page simply to give their names.

Any one who wishes to make observations on distomes in the state of 198 cercariae has only to examine some fresh-water molluscs, either the Limneae or Planorbes found in ponds; as he tears the animal to pieces on the stage of a simple microscope, he will not fail to perceive a multitude of struggling and wriggling tadpoles. Their tails twist with each other, furl up, extend, and describe arcs of circles, as if we had a nest of serpents under our eyes.

Each species of distome has it own cercariae, which are scattered among as many different inferior animals. Birds and fishes become infested by them in consequence of eating these animals.

Another distome was also found by Bilharz in the intestines of a young Egyptian boy.

Besides the distomes which inhabit the liver, there are found but few in the mammalia, except in the Cheiroptera: these insectivorous animals have their intestines literally full of these parasites. We 200 have noticed the species which regularly frequent our bats, and it only remains to discover the insects by means of which they are introduced; for it is probable that these insects are infested by cercariae during the time that they inhabit the water. Larvae and their parasites ought to be carefully studied in the localities where bats abound.

The name of Monostoma has been given to some of these trematodes which have no abdominal sucker.

The embryo, having long ciliae in front, and in the interior a sporocyst already full of young cercariae, is shown in Fig. 44. It is this latter creature which the ciliated embryo must confide to the care of others; this she puts out to nurse with some mollusc or other, until it is fit to provide for itself in its turn. We have still to discover the train by which the parasite must travel, in order to 203 arrive again at the nasal fossae which are the first cradle of the family.

We find occasionally between the feathers of some birds tubercles of the size of a pea, and when we open them we see in each two similar worms, placed so that the stomach of one is applied to that of the other; this is the monostome of which we have spoken above. These worms are from three to four millim?tres in length , and are found in the titmouse, the siskin, the sparrow, the canary, and some other birds.

The worms which naturalists call Cesto?ds, or Cestodes , have for their type the tape-worm known by every one. They are very abundant in many animals, are found in almost every class of the animal kingdom, and are almost as common as the distomians, of which we have just spoken. They are introduced into animals which are vegetable-feeders, by means of water and plants, and into carnivorous animals by their prey. The tape-worms of the herbivora lay eggs like the others, but their embryos have, as soon as they are hatched, a ciliary covering which allows them to live and 205 move about in the water. Those of beasts of prey are entirely different; it is by means of the prey that they enter their hosts. Each carnivore has its own worms, as it has its own prey which introduces them.

Independently of these worms, the vegetable-feeders afford lodging to some which are not their own.

We have found in bats two taeniae, both incompletely developed, and 206 occupying the digestive tube. One has a rostellum without hooks, like the taeniae of the vegetable-feeders, the other has hooks like those of the carnivora. These cestode parasites are observed to be of two principal forms; the first vesicular, like the finger of a glove partly drawn inwards. They are always lodged in the midst of the flesh, or in a closed organ in the middle of a cyst; under this form the cestode worm is harboured by a host which is to serve as a vehicle to introduce him into his final host. He is a parasite on a journey; he is always agamous, and usually bears the name of cysticercus . As to the second form, it is like a ribbon; it attains a great length, always occupies the intestine, attains its complete and sexual development, and lays an innumerable quantity of eggs which are disseminated with the evacuations.

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