GENERATIO ^SQUIVOCA. 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 reso- 

 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 Filaria) ; and the third in the Strongyli and 



