ENTOZOA. 



99 



with four longitudinal equidistant lines extending from the head 

 to the tail. These lines are independent of the exterior envelope, 

 which simply covers them; two are lateral, and are larger 

 than the others, which are dorsal and ventral. The lateral lines 

 commence on each side of the mouth, but, from their extreme fine- 

 ness, can with difficulty be perceived ; they slightly enlarge as they 

 pass downwards to about one-third of a line in diameter in large 

 specimens, and then gradually diminish to the sides of the caudal 

 extremity. They are occasionally of a red colour, and denote the 

 situation of the principal vessels of the body. The dorsal and ab- 

 dominal longitudinal lines are less marked than the preceding, and 

 by no means widen in the same proportion at the middle of the body. 

 They correspond to the two nervous chords, hereafter to be de- 

 scribed. 



The last species of human Entozoon which remains to be noticed 

 is the Ascaris vermicularis {Jig. 47.), a small worm, also noticed 

 by Hippocrates under the name of arrKcipig, and claiming the 

 attention of all physicians since his time as one of the most trou- 

 blesome parasites of children, and occasionally of adults, in both 

 of whom it infests the larger intestines, especially the rectum. The 

 size of the male Ascaris vermicularis is two or three lines ; that of 

 the female is five lines. 



The integument in the nematoid parasites of the human subject, 

 and in almost all the order, is more or less smooth : it consists 

 of a thin compact epidermis, and of a fibrous corium firmly attached 

 to the outer transverse muscular fibres. The epiderm is homo- 

 geneous ; i. e. it does not show the nucleated cellular structure. It 

 is impressed by minute, close-set, transverse indentations, which, in 

 some of the Nematoidea of the lower animals ( Strongylus annulatus^ 

 e. g.) are so deep as to give an annulate character to the integument ; 

 and in the Ascaris nigrovenosa the sides of the body appear thereby 

 to be fringed. Lobes, or aliform processes of the integument, charac- 

 terise certain genera and species ; e. g. the alas of Spiroptera^ the 

 finely-striated " moustaches " on the head of the Ascaris mystax, the 

 serrated membrane supported on tubercles near the tail of the same 

 worm. The corium consists of decussating fibres. The entire 

 integument is highly absorbent ; and, after death, endosmose will go 

 on to such an extent as sometimes to cause the parietes of the body, 

 if immersed in fluid, to burst. The epiderm is developed in the 

 Strongylus horridus of the water hen, into four longitudinal rows 

 of reflected booklets ; and similar spines are arranged in circular 

 groups upon the anterior part of the Gnathostoma spinigerum. 



M. Cloquet, in his elaborate monograph on the Ascaris lumhri' 



