WORMS. 209 



and the worm is set free, to crawl about in the earth until the new grain shoots 

 forth. The worm then climbs up, resting motionless whenever it gets dried, but 

 resuming its climb as soon as moisture restores its activity, and finally reaches 

 the top while the ear is young, and there entering the parts of the flower, the worms 

 cause a gall-like growth to the plant. There they dwell, and, having meanwhile 

 become mature, the eggs are developed, deposited, and hatched out. The parents 

 dying off, the embryos become the only inhabitants of the gall and form the dust-like 

 substance which we mentioned at the beginning of the paragraph. The power of this 

 species, and of its immediate congeners, to withstand desiccation and to recover their 

 full activity upon the return of moisture, is almost incredible. This wonderful capacity 

 is most developed in the larvae, the adults being endowed with less resistance. It is 

 known that one of the galls containing larvse may be kept dry for over twenty years 

 and at the end of that period be revived by moisture. Spallanzani's experiments 

 showed that the loss of moisture must be gradual, for the larva need apparently to 

 make some preparation for their long confinement. It is not to be supposed that the 

 worai dries up, but rather' that it is able to prevent its own loss of moisture for an 

 indefinite period. The excessive development of this sti-ango ability to stof) the vital 

 processes is evidently a means by which the animal is enabled to escape what were 

 elsewise the fatal dangers of its life cycle. 



The primitive type of the Nematoda is probably more nearly preserved in the 

 family of ENOPLiDiE ; they are not parasitic, but lead a free life ; for the most'part 

 they are marine animals. Very little is known of their habits or metamorphoses. 

 They are found among plants, oftentimes in snarled bunches. Some species live in 

 fresh water, but rarely, except in pure running streams, and others again in moist earth. 

 The most common genera are Enoplus and Dorylaimus. Many of the species have 

 a peculiar spinning gland at the posterior end of the body and opening on the under 

 side of the tail. " So soon," writes Professor Schik-ider, " as the animal has fixed its 

 tail upon some support, it moves along and draws out the secretion of its gland to a 

 vitreous thread several lines long. One end of the thread is glued fast, on the other 

 floats the animal in the water." Most of the Enoplidse avoid the neighborhood of 

 putrefaction, but delight in pure soils and waters, in which they often abound. 



The remaining families of the thread-worms are parasitic ; arranging them as nearly 

 as possible according to the extent they depart from the type of the free forms of the 

 class, we have, beginning with those the least changed, Filariadse, Trichotrachelidfe, 

 Strongylidffi, Ascaridse, Mermithidte, and Gordiidaj. Each of the first four of these 

 families includes parasites very dangerous to man and the domestic animals. 



Of the FiLAEiADJE the Filaria sanguinis-hommis is said to be the cause of the 

 elephantiasis, so familiar to physicians in the oriental tropics. The larvas are found in 

 the blood vessels and lymphatics of man, and by clogging the passages impede the 

 circulation and produce, it is asserted, the enormous enlargement or hypertrophy of 

 parts known as elephantiasis. It is supposed that the mosquitos suck into their own 

 bodies the larvse in the human blood ; that when the mosquitos go to the water to lay 

 their eggs, they soon die, and the worms escape into the water, these become mature 

 and produce their young, which enter the human system when the water is drunk. 

 Filaria {Dracunculus) medinensis, the so-called Guinea-worm, occurs in the tropical 

 districts of the old world, and is found parasitic in the subcutaneous tissue of man. It 

 is very thin, but may attain a length of several feet ; only the female is known. The 

 parasite lies coiled up in the soft tissue, in which it produces an ulceration, and 



VOL. I. — 14 



