CffiLELMINTHA. 103 



animals, but arranged in bundles of contractile filaments, run- 

 ning in determinate directions, and thus capable of acting 

 with greater energy and effect in producing a variety of move- 

 ments. 



In this rudimentary state, the muscular fibre does riot possess 

 the density and firmness which it acquires when completely de- 

 veloped ; it has, when seen under the microscope, a soft gelatinous 

 appearance, apparently resulting from a deficiency of fibrin in its 

 composition ; the transverse striae, usually regarded as characteristic 

 of the muscular tissue of the more perfect animals, are not yet 

 distinguishable, and the individual threads are short, passing over 

 a very small space before they terminate. On examining the 

 arrangement of these fasciculi, they are seen to be disposed in 

 two layers, in each of which they assume a different course ; thus 

 in the outer layer they are principally arranged in a longitudinal 

 direction, while the inner stratum of fibres is placed transversely, 

 affecting a spiral course, so as to encircle the viscera. From this 

 simple structure various movements result ; by the action of 

 the longitudinal fasciculi the whole body is shortened, by the 

 contractions of the spiral layer an opposite effect is produced, 

 or by the exertion of circumscribed portions of the muscular in- 

 tegument lateral flexions of the body are effected in any given 

 direction. These motions in the living worm are vigorous and 

 easily excited by stimuli ; they are therefore abundantly sufficient 

 for the purpose of progression in such situations as those in which 

 the creature lives, and enable it to change its place in the intes- 

 tines with facility. 



(140.) The nervous system of the Ascaris is strictly conformable 

 to the nematoid type. Around the mouth or anterior part of the 

 oesophagus, there appears to be a delicate nervous ring, probably 

 specially connected with the association of such movements of 

 the oral extremity as are essential to the imbibition of nourish- 

 ment. From this oral ring proceed two long nervous filaments, 

 (fig. 44, e, e,) one of which runs backwards along the dorsal 

 aspect of the body, while the other occupies a similar position 

 upon the ventral surface. The last-named filament is described 

 by Cloquet as dividing in the female Ascaris, at the point where 

 the termination of the organs of generation issue from the body 

 (fig. 44, w), so as to enclose the termination of the vagina in a 

 nervous circle. 



(141.) The digestive apparatus in this order of intestinal worms is 



