CESTODA. 



3*3 



PLATE XIV. 



CESTODA: HYDROIDEA. 



THE figures I to 5 are intended to show diagrammatically the life- 

 history of one of the typical Cestoda, genus Taenia. Figure i represents 

 the sexual animal as it is found in the segmented form, called * strobila ' 

 from the analogy of a fir-cone, in the intestinal canal of a carnivorous or 

 omnivorous vertebrate * host,' such as the dog, or human subject. Figure 2 

 represents the distal half of a segment, or * proglottis,' as it may be seen 

 before the great accumulation of ova in the uterus has caused the dis- 

 appearance of the other sexual organs, male and female, which each seg- 

 ment contains. Figure 3 represents a ripe segment, so distended with 

 embryos as to have caused the ripe proglottides, which retain considerable 

 locomotor powers, to be called ' ovaria ambulantia.' Figure 4 shows one 

 of the microscopic embryos, the so-called * proscolex,' as it appears when 

 set free from its shell within the stomach, into which it is introduced. 

 Figure 5 shows the cystic stage or scolex into which such a proscolex as 

 that shown in Figure 4 developes, when it belongs to Taenia coenurus, 

 which differs from most other Tapeworms in having its proscolex prolife- 

 rating as drawn in the figure, instead of producing a solitary * new head ' or 

 ' scolex.' This cystic stage is passed in the tissue of some solid organ, such 

 as the liver or the muscles ; but in the particular case of Taenia coenurus, 

 most usually in the brain of the sheep, though sometimes in other parts of 

 the body of this ruminant, as also of rodents. 



FIG. i. Tapeworm, as found in the intestinal canal of man or of a dog, semi-diagrammatic; 

 after Van Beneden, Memoire sur les Vers Intestinaux, Paris, 1858, PI. xxvi. Fig. 25. 



THE * head ' or ' nurse ' so-called is armed with a circlet of spines, 

 as is the case with Taeniae which are harboured in the intestines of birds 

 and of carnivorous mammals ; whilst the Taeniae of Amphibians and 

 herbivorous mammals are not possessed of this armature. Posteriorly to 

 the circlet of spines is seen a circlet of four suckers. An unsegmented 

 neck follows the suckers. The first segments are small, but as the dis- 

 tance from the head increases, so their size and development increase. 

 A Tapeworm is not a colony composed of an asexual head and sexual pro- 

 glottides or segments. The segmentation of the body is probably acquired, 

 and not primitive as generally supposed. 



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