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 Amabæ, 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 psorospermia. We give the representation (Fig. 74) of gregarinæ which we have found abundantly on the Nemertes; and Fig. 74.-Gregarinæ of Nemertes Gesseriensis. Fig.75.-Stylorhynchus oligacanthus, from the larva of the Agrion. (Fig. 75) a peculiar species which lives in the larva of an agrion. We also give a sketch (Fig. 76) of some very remarkable parasites, whose affinities are still problematical, and which only inhabit spongy bodies, such as the Fig. 76. -Dicyema Krohnii, from Sepia officinalis. kidneys of cephalopods. The name of Dicyema has been given to them. Prof. Ray Lankester has quite recently made some very interesting observations, at Naples, on these problematical beings; and my son has just devoted a part of his vacation, with two of his pupils, to elucidate the points of their organization and development, which are still obscure. He went to reside at Villefranche, near Nice, in order to obtain fresh cephalopods every day. His observations have led him to a result quite different from that which I expected. CHAPTER X. PARASITES DURING THEIR WHOLE LIFE. In this chapter we bring together true parasites, which may be called complete; they pass every part of their life under the care of a neighbour, and require an asylum the more urgently, since they cannot exist without it. They absolutely need both food and lodging. Not long ago, all parasites were supposed to be dependant during their whole life, and to be incapable of living outside the body of another animal. We have before proved that this opinion was erroneous. We find in this category a great number of parasites which may be separated and placed in the first group, including all such as pass all the phases of their life on the same animal, without changing their costume, and many of which never leave the fur, the feathers, or the scales, among which they are born. Fishes nourish on the surface of the skin a great number of these, which helminthologists have thought proper to classify under the name of Ectoparasites. Among many crustaceans and insects, only one of the sexes is parasitical. The males remain entirely free, and preserve all their attributes, while the females seek for assistance, and require food and lodging. The female alone sacrifices her liberty, and changes her form entirely in order to secure the preservation of her posterity. The insects called Strepsiptera, which live as parasites on wasps, furnish a curious example of this (Fig. 77). These insects, the Polistes, the Andrenæ, and the Halicti, do not kill the larvæ of the Hymenoptera on which they feed; they suck the blood of their victim slowly, and leave him just enough strength to go through his metamorphoses. The females are condemned to remain almost completely immovable on their prey, while the males are winged. Naturalists have paid great attention to these latter insects, as much on account of their mode of life as of the difficulties which they have suggested to entomologists in the appreciation of their natural affinities. Are they coleoptera, as was for a long time, and perhaps correctly, Fig. 77.-Stylops. Male, natural size, and magnified. supposed, or do they form a distinct order by themselves? However this may be, these are the facts known concerning them, according to the recent observations of Mons. Chapmann, a conscientious naturalist. The females do not lay their eggs in the nests of wasps, but the larvæ, under the form of meloë, penetrate into the cells, by the assistance of the larvæ of the wasps, which carry them hidden between the second and third ring. The |