ENTOZOA. 



101 



middle line of that aspect of the body corresponding to the ventral 

 ^g chord on the opposite aspect.* 



In the Linguatula tcenioides {Jig. 45.), a propor- 

 tionally large ganglion {g) is situated immediately 

 behind the mouth, and below the oesophagus, which 

 is turned forward in the figure at o : small nerves 

 (h, i, k) radiate from this centre to supply the mus- 

 cular apparatus of the mouth and contiguous pre- 

 hensile booklets ; and two large cords (/, /) pass 

 backwards, and extend along the sides of the ab- 

 dominal aspect of the body to near the posterior 

 extremity, where they expand and are lost in the 

 muscular tissue, t There is also a stomato-gastric 

 system, represented by four small but distinct gan- 

 glions situated on the under part of the oesophagus, 

 from which minute filaments extend along the ali- 

 mentary canal. J I have already alluded to the evi- 

 dences of the nervous system afforded by the ocelli 

 in the young of some species of Trematoda, and in 

 the full-grown Polystoma of the urinary bladder of 

 the toad and frog. We have as yet no evidence 

 that any species of Ccelelmintha possesses rudimental 

 organs of vision at any stage of existence. 



The digestive organs are very simple, and are 

 subject to little variety in the Nematoid worms ; 

 an ample alimentary canal, suspended to the pa- 

 rietes of an abdominal cavity, extends in nearly a 

 straight line from the mouth to the anus, which are 

 at opposite extremities of the body. 



In the Filaria the mouth is a simple circular pore, 

 sometimes surrounded by a circle of radiated papillae ; 

 a short and slender oesophagus suddenly dilates into 

 the stomach, which is fusiform, and indicates the be- 

 ginning of the intestine by its posterior contraction. 

 Nervous s d '^^^ mouth of the Trichocephalus dispar is small 



female organs of ge- and orbicular ; the oesophagus is narrow and short; 



neration. . . 



Linguatula, the intestinal tube is narrow and sacculated where 

 °"^'"'' ■ it occupies the filiform division of the body, dilated 



* This arrangement is denied by Siebold, who confirms only that above de- 

 scribed in the Strongylus ; and he does not hesitate to declare : — " Die Abbildung 

 eines doppelten Ners-enfaden, welcher sich nach Grant (Outlines of Comp. Anat., 

 p. 186. fig. 82. A.), durch den Leib von Ascaris hinziehen soil, ist wol nur eine 

 ideale Zeichnung." XXIV. p. 126. 



t LXXXVII. p. 328. pi. 41. figs. 12, 13. % XCH. 



H 3 



