NEMATOID ENTOZOA. 531 



face ; but these would seem destined, not so much to give motion 

 to the body, as to renew the stratum of fluid in contact with it ; 

 for such change of place as the animal does exhibit, is effected 

 by the contractions and extensions of the body generally, as in 

 the Amoeba ( 261). A sort of " conjugation" has been seen to 

 take place between two individuals, whose bodies, coming into 

 contact with each other by corresponding points, first become 

 more globular in shape, and are then encysted by the formation 

 of a capsule around them both ; and the partition walls between 

 their cavities disappear ; and the substance of the two bodies be- 

 comes completely fused together. As the product of this con- 

 jugation, there are first seen a number of globules or cell-like 

 bodies ; and these gradually assume a form so like that of Navi- 

 culce ( 184) as to have been mistaken for them ; their walls, 

 however, are destitute of silex, and there is no further resem- 

 blance between the two kinds of bodies, than that of figure. 

 These " pseudo-naviculae" are set free, in time, by the bursting 

 of the capsule that encloses them ; and they develope themselves 

 into a new generation of Gregarinse, first passing through an 

 Amcebo-like form. .It appears, however, that the " pseudo-navi- 

 culse" or "psorosperms" may be also formed by the simple 

 division of the granular matter of a single Gregarina body, with- 

 out any conjugation. 1 



359. The higher forms of Entozoa, belonging to the " nema- 

 toid" or thread-like order of which the common Ascaris may 

 be taken as a type, one species of it (the A. lumbricoides, or 

 "round worm") being a common parasite in the small intestine 

 of man, while another (the A. vermicularis, or "thread worm") 

 is found rather in the lower bowel, approach more closely to 

 the ordinary type of conformation of Worms ; having a distinct 

 alimentary canal, which commences with a mouth at the anterior 

 extremity of the body, and which terminates by an anal orifice 

 near the other extremity ; and also possessing a regular arrange- 

 ment of circular and longitudinal muscular fibres, by which the 

 body can be shortened, elongated, or bent in any direction. The 

 smaller species of Ascaris, by some or other of which almost 

 every Vertebrated animal is infested, are so transparent, that 

 every part of their internal organization may be made out, 

 especially with the assistance of the " compressor," without any 

 dissection ; and the study of the structure and actions of their 

 generative apparatus has yielded many very interesting results, 

 especially in regard to the first formation of the ova, the mode 

 of their fertilization, and the history of their subsequent deve- 

 lopment. Some of the worms belonging to this group are not 

 parasitic in the bodies of other animals, but live in the midst of 

 dead or decomposing vegetable matter. The Crordius or hair- 

 worm, which is peculiar in not having any perceptible anal 



1 For the most recent information on this point, see a memoir by M. Nat. Lieberktihn, 

 in Mem. de 1'Acad. Roy. de Belgique, torn. xvi. 



