CHAPTER XXV 



CESTOIDEA 



Cestoidea — History — Morphology — Life-History — Habitat — Classification — 

 Cestodes in man — References. 



CESTOIDEA RuDOLPHi, 1808. 



Definition. — Platyhelmia without alimentary canal in any stage 

 of the life-cycle, with segmented body, in which the epidermis, which 

 has sunk into the parenchyma, secretes a thick cuticle. Lime- 

 secreting cells are developed in greater or less number, and form 

 calcareous concretions. Organs of fixation of a variable character are 

 developed. The habitat of the adult worm is typically the intestine, 

 and that of the larVal form some other part of the body, normally 

 that of another host. 



History.- — It is believed that cestodes were known to the ancients, 

 and that the reason why Moses, who figures largely in the history 

 of Tropical Medicine, forbade the Israelites to eat pigs and such 

 animals, was because of the parasites known to exist in their flesh. 



Aristotle knew the proglottides of tapeworms, and as early as 

 1592 Tcenia was distinguished irom Bothriocephalus. Tyson (1683) 

 discovered the head of the tapeworm of a dog. Redi (1687-1705) 

 came to the conclusion that Cysticerci were animals, and Zeder 

 (1800) formed them into a separate group, Cystici ; but Kiichen- 

 meister in 1851 proved by feeding experiments that these were only 

 the larvae of tapeworms, and that, as a rule, two different kinds of 

 animals were required as hosts in order that the life-cycle might 

 take place. 



Leuckart, Braun, Fiihrmann, Looss, Sonsino, Grassi, Blanchard, 

 von Linstow, Liihe, Stiles, Leiper, and Sambon may be mentioned 

 as investigators who have greatly improved our knowledge of these 

 parasites. 



Morphology.— There are two groups of cestodes, one called the Cestodaria 

 containing genera with only a single segment, and another Cestoda, in the 

 restricted sense of the word, which includes all forms possessing a scolex and 

 segments. It is with this latter group that we are now concerned. 



The true cestodes are easily recognized by their band-like segmented body, 

 which is usually of a white colour. They are broad and large posteriorly, 

 becoming narrower and narrower till the place is reached where they are 

 attached to the intestinal wall. This anterior end is called the ' scolex,' while 

 the segments are called ' proglottides.' The scolex is divisible into a broader 

 anterior portion called the head, and a narrower posterior portion, the neck. 



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