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CHAPTER VI. 

 HUMAN TAPEWORMS. 



Cestoda, or Tapeworms, differ from the Trematoda in 

 that (i) there is no alimentary system, food being derived 

 by absorption through the cuticle ; (2) there is a single 

 fixative apparatus situated at the anterior extremity of 

 the body ; and (3) they are divided into segments, each 

 segment being a distinct hermaphrodite animal. There is 

 a common nervous, circulatory (water vascular) and mus- 

 cular system. They are easily distinguished from trema- 

 todes by their length, flattened, tape-like appearance, and 

 by the segmentation. 



The Cestodes are divided into two great classes, re- 

 presented by the Pseudophyllidice (Dibothriocephaloidea) 

 and the Cyclophyllidice (Tceniidce). This separation was 

 made on the differences of cephalic armature. That of 

 the Pseudophyllidice consists of two slit-like, elongated 

 depressions, and of the Cyclophyllidiae of four round 

 suckers, and a rostellum, with, in some cases, hooklets in 

 addition. 



The separation is a sound one, and can equally be 

 made on the life-history, particularly the method of 

 development. The development of the Dibothriocepha- 

 loidea is comparatively simple : the embryo contained in 

 the egg becomes the larva, and this larva forms the 

 scolex of the' adult, whilst in the Cyclophyllidiae the 

 embryo is converted into a cyst, and the embryonic head 

 is lost. In the interior of this cyst one or more secondary 

 larval heads are formed, so that asexual multiplication 

 may occur. These larval heads, produced asexually, 

 become- scolices of the adults and the embryonic head 



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