These worms, when they approach the adult and sexual age, lose their various external organs, and are so completely modified with respect to their organization, that at last they are merely a case for eggs. They are so entirely egg-cases, in which the digestive tube and the other organs disappear in proportion as the sexual organs are 181 developed, that many naturalists have taken these worms for a simple ovisac. This has also been the case with the _Nematobothrium_ of the fish known under the name of the eagle-fish; it has been taken by an eminent naturalist for a nest of psorospermiæ. There are also worms which take refuge in plants, and live at their expense, as if they were in an insect. One of the most remarkable is that which attacks corn, and produces the disease known by the name of smut, the corn eel (_Anguillulina tritici_). It is a very small and thin cylindrical worm, which dries up completely with the grain of corn which has nourished it, and which can remain for an indefinite period without dying, in a state resembling dust. Every time that it is moistened, it resumes its activity. This return to life has been compared to a kind of resurrection. Mons. Davaine has studied this worm with great care; he has made known the different phases of its development, and the manner in which it introduces itself into the plant and the grain. Needham, in his "New Discoveries made with the Microscope," (1747) gives a whole chapter to these microscopic eels. The larvæ of the _Anguillula scandens_ are dried in the galls inhabited by the mother. As soon as these galls fall and grow moist, the larvæ revive, and abandon their cradle to live in freedom. Soon after this, they go in search of their plant, take it by storm, and penetrate into the tissues before the period of fecundation; having become sexual in the interval, these microscopic nematodes lay their eggs in a nest formed at the expense of the plant. Another species lives in the _dipsacus_, in which also it produces 182 disease (_Anguillulina dipsaci_). It attacks the flowers, and remains on them without signs of life till the moment that they are moistened. The vinegar eel is another nematode worm which has some affinity with the preceding ones. It has been considered a _Rachitis_. There exists also a river species; but have not different worms been confounded under this name? Many species live in brackish water, and these are remarkable for the presence of bristles on their heads, and by very distinct eyes. [3] The discovery of a free bothriocephalus at the bottom of a ditch caused a great sensation in the world of naturalists some years ago. It was then thought that the parasite could not exist except in the body of an animal: they could only imagine it shut up as in the cells of a gaol. [4] Missionary Travels in South Africa, p. 136. CHAPTER IX. 183