TREMATODA I2Q 



ciliated in the larval condition, 1 and in their adult state are covered with 

 a cuticle, the matrix cells of which are sunk into the parenchyma. They 

 have either one, a few, or several sucking discs, and frequently also possess 

 chitinous clasping [suckers with chitinous armour] and clinging organs [hooks]. 

 The intestine is simple, but generally bifurcated, and not rarely there are trans- 

 verse anastomoses between, or blind ducts at the branches of, the fork. 

 Excretory organs double, with two orifices at the anterior extremity or a simple 

 one at the posterior end. [The two trunks usually open into a common 

 contractile vesicle, which opens at the posterior end of the body. F. V. T.] 

 Development takes place by a metamorphosis or alternation of generations. 

 These worms are almost always hermaphroditic; with two [Polytomum and 

 most Monogenea] or several female and one male sexual orifices.- They live, 

 almost without exception, as parasites on vertebrate animals, but the inter- 

 mediatry generations are passed in molluscs, 



Class III. Cestoda (Tape worms). Endoparasitic flat worms without an 

 alimentary canal. The larval stages are rarely ciliated, but are usually provided 

 with six hooklets ; the adult worm is covered with a cuticle, the matrix 

 cells of which are sunk into the parenchyma. The body is either simple 

 (Cestodaria), or composed of a chain of segments, in which case it consists of the 

 scolex, and the segments containing the sexual organs '(Proglot tides) (Cestodes 

 s. str.). The scolex is provided with various sucking and clinging organs, and 

 there are calcareous bodies in the parenchyma. Excretory organs symmetrical, 

 opening at the posterior end. These worms are almost always hermaphroditic, 

 and trien possess one or two female and one male sexual orifice. During 

 development a larval intermediary stage termed " cysticercus " appears 

 which almost always lives as the sexual animal in another host. The 

 adult stage is parasitic in vertebrate animals and the larval stage in 

 invertebrates. [This is not always the rule, for this cyst stage occurs 

 abundantly in vertebrates, such as Cysticercus celluloses in the pig, Cysti- 

 cercus pisciformis in rabbits, &c. F. V. T.] 



Class I. T*ematoda, Rud. 



These worms are usually leaf- or tongue- shaped, rarely barrel- 

 shaped or conical ; they vary from 0*1 mm. to almost i m^^Tn 

 length; most of them, however, are small (5 15 mm.). The sur- 

 face on which the orifice of the uterus and the male sexual 

 opening are situated is termed the ventral surface ; the oral 

 aperture, which also acts as anus, is always at the anterior end,. 

 except in the genus Gasterostomum, which is parasitic in fishes. 



Sucking discs are common and occur in varying numbers and 

 positions at the anterior and posterior extremities as well as on the 

 ventral surface, and occasionally on the lateral border and on the 



1 [An exception to this occurs in Temnocephala, in which the skin, especially on the 

 surface of the tentacles, is provided here and there with cilia. F. V. T.] 



2 [In Diplozoon and one or two other forms the vagina is unpaired. F. V. T.] 



9 



