VERMES. 55 



These worms are mostly entozoic ; they have generally a body- 

 cavity and a distinct nervous system. Eye-specks or ocelli are 

 frequently present. The water-vascular system assumes many 

 forms, but is sometimes wanting Development is mostly direct. 



Schmarda includes Chaetognatha in this class. About 1400 

 species are known. They are divided into two orders : 



With a body-cavity NEMATODA. 



Without a body-cavity ACANTHOCEPHALA. 



Order I. NEMATODA. 



COZLELMINTHA. NEMATELMINTHA. 



Mostly internal parasites, with thread-like or cylindrical non- 

 ciliated bodies. No respiratory nor circulatory organs. Sexes 

 distinct. 



These have a distinct mouth and intestine, although in some 

 Gordiidse they are either rudimentary or wanting. Anguillulidae 

 and Enoplidse have no nervous system. A few are subject to 

 metamorphosis ; thus a Urolabes-form is the larva of Filaria, and 

 a Rhabditis-form of Dochmius. Ascaris, and probably some others, 

 are dimorphous. The young cast their skins before arriving at 

 maturity. 



The Gordiidae are sometimes ranked as an order ; Gordius itself 

 leads at first a free existence in water, but soon finds its way into 

 some aquatic insect. Its species are sexless so long as they are 

 parasitic. Mermis is found in Lepidoptera, and Spharularia 

 bombi in the humble bee. The female of the latter, formerly mis- 

 taken for the male, has the uterus 28,000 times larger than her- 

 self ; this uterus was supposed to be the female. This excessive 

 development of the uterus in some of these worms causes the obli- 

 teration of the ordinary opening ; and the young only escape by 

 the bursting of the maternal body. 



Anguillula are found in stale paste, vinegar, ears of wheat 

 affected with blight, &c. ; while some of them cause galls on 

 plants. The too well-known guinea- worm (Filaria medinensis) 

 varies from six inches to ten or twelve feet in length, but is 

 scarcely two thirds of a line in thickness. Synganius trackealis 

 is found in the trachea of birds, and is the cause of the " gapes." 

 Among the parasites in man may be mentioned Ascaris lumbri- 

 coides and Trichina spiralis, the latter getting in millions into the 

 muscles, and causing the disease called trichinosis or trichiniasia ; 



