GENERATIO 7EQUIVOCA. 319 



a chitinous substance ; the muscles are principally formed of lon- 

 gitudinal fibres, whilst transverse fibres are never wanting ; 

 the parenchyma appears to be rich in vacuoles, whence results the 

 great inflation of these worms in water; on the sides there are 

 sometimes a few longitudinal lines, upon the signification of which 

 we shall speak under Oxyuris vermicularis ; a nervous system cer- 

 tainly occurs in them, although it had hitherto been overlooked, 

 and has recently been detected with certainty only in certain 

 Oxyurides, and I believe I have found parts of it also in Tricho- 

 cephalus ; the alimentary canal is divided into a muscular oeso- 

 phagus and stomach, a thin-walled intestine partly furnished with 

 epithelium, and an anus; the sexual organs are divided between two 

 different individuals ; the orifice of the vagina lies rather anteriorly, 

 and that of the male sexual organs more towards the posterior 

 end. Peculiar clasping organs are found in the species of Strongy- 

 lus. A ventral sucker, which occurs in certain Oxyurides, appears 

 not to be possessed by 0. vermicularis. The penis is sometimes 

 simple, sometimes double, and sometimes lobed. It is not per- 

 forated, as in the Cestodea and Distoma, and if it had been per- 

 forated, it would have required a much greater lumen, and conse- 

 quently a much greater calibre, on account of the nature of the 

 spermatozoa. For whilst, in the Distoma, for instance, the 

 spermatozoa are always^ seen moving in the form of simple threads, 

 in the Nematoida they are observed to be of a more or less 

 globular form. To transfer these globular structures into the 

 vagina, all that is required is a hollowed furrow, in which the 

 seminal globule, if I may express myself so, rolls forward, just as 

 the ball is rolled back in a skittle-alley, from the person who 

 attends to the setting up of the skittles, to the players. In this 

 it is of no consequence whether the ball runs on a furrow which 

 is formed out of one piece, like the channel on the gable of 

 a house, or between two longitudinal laths directed obliquely 

 towards one another, but do not completely touch at their point 

 of greatest convergence, as may be seen, for example, if we allow 

 a billiard-ball to roll forward upon two cues, or in a furrow com- 

 posed of several laths, placed together in such a way that they 

 actually form an angular, but yet a nearly semicircular space, in 

 which the ball rolls forwards. The first of these three kinds of 

 furrows occurs in the worms with a simple penis [Oxyuris, Tri- 

 chocephalus) ; the second in those with a double, non-lobate 

 penis [Ascaris and Filai'ia) ; and the third in the Strongyli and 



