CHAMBERS'S INFORMATION FOR THE PEOPLE. 



DIVISION I. VERMES 



(Worms), in which the division of the body into 

 longitudinally arranged segments is not apparent, 

 or but imperfectly marked ; and there is an 

 absence of appendages jointed or articulated to 

 the body. 



CLASS (A). Platyelmia, or Flat-worms, are usu- 

 ally flattened and ovoid in form, and the segmen- 

 tation of the body is not distinct. The nervous 

 system consists of a pair of ganglia, situated at the 

 anterior extremity of the body, from which fila- 

 ments arise and pass backwards. Some live in 

 the interior of other animals, and are parasitic ; 

 while others are covered with cilia, and swim 

 freely in the water. 



ORDER i. Cestoide a including the family of 

 the Taniada, or Tape-worms, which are parasitic 

 in the intestinal canal of warm-blooded vertebrata. 

 The mature worm is ribbon-like, and consists of 

 many joints or segments, which resemble each 

 other. The anterior segment, or head, has a circle 

 of hooks and suckers by which it is enabled to fix 

 itself to the intestinal canal of its ' host.' The 

 various segments are produced by a process of 

 budding from the head posteriorly, so that the 

 oldest and most mature are farthest removed from 

 it, each new bud being formed between the head 

 and the last-formed segment. As neither mouth 

 nor digestive system is pres- 

 ent, the animal is nourished 

 by absorption through the soft 

 skin of the body. Running 

 down along each side is a 

 vessel, which communicates 

 with its fellow by a branch at 

 the posterior part of each seg- 

 ment This is described as a 

 water-vascular system, but in 

 none of the Vermes is it ever 

 used for purposes of progres- 

 sion. Each segment, except 

 the head, is provided with 

 male and female sexual or- 

 gans. The female organ con- 

 sists of a branched tree-like 

 tube, occupying nearly the 



whole f each . se S ment > which 

 opens along with the male duct 



at the apex of a little elevation 

 magnified; placed on the margin or sur- 

 f ace of the segment The de- 

 velopment of these animals 

 presents some most remarkable 

 phenomena. Sexually mature 

 segments can only be formed in the intestinal 

 canal of a warm-blooded vertebrate ; but the 

 development of an embryo cannot go on unless 

 the ova are introduced into the intestinal canal 

 of some animal other than the one in which the 

 mature segments were produced ; so that the 

 segments with ova have to be expelled from the 

 bowel. The joints, after expulsion from the 

 bowel, decompose, and liberate the ova, which, 

 when swallowed by another warm-blooded verte- 

 brate, give rise to an embryo which is provided 

 with spines suited for boring. With these it 

 perforates the 'wall of the stomach, and reaches 

 some solid organ, such as the liver or brain, 



140 



Tape-worm 



of the sucking discs; 

 d, the neck. 



where it develops for itself a bag or cyst, and 

 is said to become encysted. In this condition 

 it is composed of a ' head ' furnished with hook- 

 lets, and a vesicle filled with fluid at its poste- 

 rior extremity; but it has no generative organs. 

 These are the so-called cystic worms, whose 

 presence in the brain of sheep gives rise to the 

 disease called 'the staggers.' Unless the organ, 

 such as the liver or brain, containing these 

 cystic worms is swallowed by some other warm- 

 blooded vertebrate, they undergo no further 

 development. When swallowed, their vesicle 

 disappears, and buds are given off from their 

 posterior extremity, which develop organs of re- 

 production, and constitute the segments of the 

 adult worm. The ordinary tape- 

 worm met with in the intestinal 

 canal of man in this country is 

 Ttznia soltum, which sometimes 

 measures several yards in length. 

 The cystic form of this species is 

 called Cysticercus celluloses. It 

 is found in the muscles of the 

 pig, constituting what is known 

 as measly pork If a portion of 

 this is eaten by man, the cystic 

 form develops itself in his intes- 

 tinal canal into a tapeworm. 

 Another tape-worm common in 

 man is the Tcenia medio-canel- 

 lata, which is derived from the 

 ' measles ' of the ox. Fluke-worm (Dis- 



ORDER 2. Trematoda are toma hepaticum). 

 parasitic, and include the Dis- 

 toma hepaticum, or ' fluke,' which infests the liver 

 of sheep, and gives rise in them to the disease 

 called 'rot.' The body is flat and oval in form, 

 being furnished with two suckers to enable it to 

 adhere to its host 



CLASS (B). Nematelmid) or round-worms, are 

 nearly all parasitic and unisexual. The body 

 is rounded and elongated, and has an annulated 

 appearance. 



ORDER 3. Gordiacea, or hair-worms, distin- 

 guished by their great length, sometimes make 

 their appearance in enormous numbers in par- 

 ticular places, and give rise to the phenomenon 

 of ' worm-showers.' 



ORDER 4. Nematoda are free or parasitic. 

 Type Ascaris lumbricoides, or round-worms of the 

 human subject, is elongated 

 and cylindrical in form, and 

 has a wrinkled appearance. 

 An alimentary canal and dis- 

 tinct anus are present. The 

 sexes are distinct, The ner- 

 vous system is in the form of 

 a ring encircling the gullet, 

 giving branches forwards and 

 backwards. The Thread- 

 worms (Oxyuris), which are 

 so troublesome to children, 

 belong to this group. The 

 Guinea-worm (Filaria medi- 

 nensis) lives in the cellular Trichina spiralis spir- 

 tissue under the skin chiefly ally coiled within its 

 of the legs. It is often several cyst. (From Kiichen- 

 feet long ; and is common in meister's Parasites.) 

 tropical Africa. 



In the muscles of the human subject, coiled up 



