WORMS. 209 



:niil 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 to]) 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, iiaving meanwhile 

 become mature, the eggs are develo]ied, deposited, and hatched out. The parents 

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

 substance whicli we mentioned at the begiiniing of the paragrapli. 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 larvie, the adults being endowed with less resistance. It is 

 known that one of the galls containing larva; may be kejit 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 tlie Lirva; need apparently to 

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

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

 indefinite ])eriod. Tlie excessive development of this strange ability to stop 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 jirobably more nearly preserved in i\w 

 family of Enoplid.e ; they are not parasitic, but lead a free life ; for the most jjart 

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

 They are found among plants, oftentimes in snarled bunches. Some s])eoies live in 

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

 The most common genera are Enoplns and Dorylabtnis. 3Iany "f the sj^ecies have 

 a jjeculiar spinning gland at the posterior end of the body and opining on the under 

 side of the tail. "So soon," writes Professor Schneider, "as tlir niiimal has fixed its 

 tail upon some support, it moves along and draws out the s(cv(ii<iu 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 EnoplidiB avoid the neighborhood of 

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



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

 as ])ossible according to the extent they depart from the type of the free forms of the 

 class, we have, beginning with those the least changed, Filariadie, Trichotrachelidaj, 

 Strongylidae, AscaridiB, Mermithidc'e, and Gordiidie. Each of the first four of these 

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



Of the F1LARIAD.E the Filaria sanguinis-hominis is said to be the cause of the 

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

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

 circulation and produce, it is asserted, the enormous enlargement or liyi)ertrophy of 

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

 bcMlies the larvae 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 {Dracuncidus) mediiietisis, the so-called Guinea-worm, occurs in the tropical 

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

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

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

 VOL. I. — 14 



