262 THE ANIMAL PARASITES OF MAN 



Some nematodes live free in fresh or salt water, in soil, mud, or decaying 

 vegetable matter, others parasitically in the most various organs of animals, 

 as well as frequently also in plants. 



(a) ANATOMY OF THE NEMATODES. 



All the Nematodes are covered by a CUTICLE, which in the 

 small species is thin and delicate, while in the larger species it 

 is thickened, and may consist of several layers of complicated 

 structure. 1 Porocanals do not occur. According to general opinion, 

 which is confirmed by the history of development, the cuticle is a 

 product of the epithelium that had formerly existed or is still found 

 beneath it ; in young specimens and small species it is perceptible, 

 but in older worms it frequently alters so considerably that not only 

 do the borders of the cells disappear, but a fine fibrous differentia- 

 tion appears in the plasm. The matrix or hypodermis then has the 

 appearance of a connective tissue strewn with nuclei, so that it 

 is hardly distinguishable from the texture of the cutis, which is 

 always present, though it may be but feebly developed. 2 It is 

 the cutis alone which projects crest-like, and which forms the 

 above-mentioned lateral and median ridges (fig. 182). 



Unicellular cutaneous glands are known in parasitical as well 

 as in free living species ; they vary in number and arrangement, 

 and are found discharging some at the anterior extremity, and 

 others in the vicinity of the genital orifices. In other cases large 

 numbers of them are present along the lateral ridges ; they are 

 strongly developed in most of the Trichotrachelidae, where they 

 discharge either along a part of the ventral surface or. along the 

 lateral and median ridges ; they are placed so closely together that the 

 ridges of the cuticle perforated by the orifices have long been known, 

 and have been described as " rodlet borders," or " fields of rods." 3 



As the cutis is immediately adjacent to the dermo-nmscular tube, 

 the simple layer of the muscular cells is by the longitudinal ridges 



1 Bommel, A. v., " Ueber die Cuticularbildung bei Nemat." (Arb. zool.-zoot. Instil. 

 Wiirzburg, 1895, x -> P- 189.) Toldt, C., " Ueber den feinen Bau der Cuticula bei Ascaris 

 megalocephala " (Arb. aus d. zool. Inst. Wien., 1899, xi., p. 289). 



- The subcuticular stratum of the nematodes certainly requires further investiga- 

 tion. L. Jammes considers it nervous (" Contrib. d I' etude de la couche sous-cuticu- 

 laire des Nemat." An. sc. nat. Zool., 1892,. Ser. vii., vol. xiii., p. 321), and M. 

 Condorelli-Francaviglia does not find the hypodermis cells in epithelium-like order, but 

 separated by a granular-fibrillary mass, which entirely resembles the substance of 

 the deeper-lying layers of the cuticle (" Ric. zool. ed. anat.-ist. sulla Filaria labiata," 

 Boll. soc. rom. stud, zool., 1895, iv -> PP- 93 an d 248). 



3 Jagerskiold, L. A., " Weit. Beitr. z. Kenntn. d. Nemat." (Kgl. Sv. Vet.-Ak. Handl., 

 1901, xxxv., No. 2.) 



