ANNULOSA, OK WORMS. 193 



times in groups; but upon careful examination each vesicle is found to 

 bear upon some part a 'head' furnished with booklets and suckers; and 

 this may be either single, as in Cysticercus (the entozoon whose presence 

 gives to pork what is known as the ' measly ' disorder), or multiple, as in 

 Cmnurus, which is developed in the brain, chiefly of sheep, giving rise 

 to the disorder known as ' the staggers.' Now in none of these Cystic 

 forms has any generative apparatus ever been discovered, and hence they 

 are obviously to be considered as imperfect animals. The close resem- 

 blance between the ' heads' of certain Cysticerci and that of certain Tcenice 

 first suggested that the two might be different states of the same animal; 

 and experiments made by those who have devoted themselves to the work- 

 ing-out of this curious subject have led to the assured conclusion, that 

 the Cystic Entozoa are nothing else than Cestoid Worms, whose develop- 

 ment has been modified by the peculiarity of their position, the large 

 bag being formed by a sort of dropsical accumulation of fluid when the 

 young are evolved in the midst of solid tissues, whilst the very same 

 bodies, conveyed into the alimentary canal of some carnivorous animal 

 which has fed upon the flesh infested with them, begin to bud-forth 

 the generative segments, the long succession of which, united end-to-end, 

 gives to the entire series a Worm-like aspect. 



591. The .higher forms of Entozoa, belonging to the Nematoid 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. ver- 

 micularis, 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 arrangement 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 ( 125) 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 development. Some of the Worms belong- 

 ing to this group are not parasitic in the bodies of other animals, but live 

 in the midst of dead or decomposing Vegetable matter. The Gordius or 

 'hair worm,' which is peculiar in not having any perceptible anal orifice, 

 Beems to be properly a parasite in the intestines of water-insects; but it 

 is frequently found in large knot-like masses (whence its name) in the 

 water or mud of the pools inhabited by such insects, and may apparently 

 be developed in these situations. The Anguillulce are little eel-like worms 

 of which one species, A. fluviatilis, is very often found in fresh water 

 amongst Desmidiece, Confer VCB, etc., also in wet moss and moist earth, and 

 sometimes also in the alimentary canals of snails, frogs, fishes, insects, 

 and larger worms; whilst another species, A. tritici, is met-with in the 

 ears of Wheat affected with the blight termed the 'cockle;' another, the 

 A. glutinis, is found in sour paste; and another, the A. aceti, was often 

 found in stale vinegar, until the more complete removal of mucilage and 

 . the addition of sulphuric acid, in the course of the manufacture, ren- 

 dered this liquid a less favorable ' habitat ' for these little creatures. A 

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