iS8 



WOJiMS. 



of generations." It is doubtful, however, what term should 

 he applied to those cases in which the bladderworm {Cmnurus 

 and Echinococcus), forms not one head only but many, each 

 of which is capable of becoming an adult tapeworm. The 

 only known exception to the fact that sexual tapeworms are 

 parasites of Vertebrates, is Archigeies Sieboldii, a simple 

 cestode which is sexual within the small fresh-water worm 

 Tubifex rivulorum. 



General Characters. — With the conditions of endopara- 

 sitic life, we may associate the occurrence of fixing-organs 

 (suckers, and usually hooks as well), the absence of sense- 

 organs, the low though somewhat complex nervous system 

 (lateral nerve-cords and anterior ganglionated commissures), 

 the entire absence of a food-canal, the absorption of food 

 through the skin, and finally, the prolific multiplication. 



The body-cavity is represented only by spaces. The 

 excretory system consists of fine branches ending with ciliated 

 funnels in the above-mentioned spaces, and connected with 

 larger longitudinal vessels which have transverse bridges 

 at each joint and a terminal pore. 



The male reproductive organs include diffuse testes, a vas 

 deferens, and a protrusible terminal cirrus. The female 

 organs include a pair of ovaries, yolk-glands, a shell-gland, 

 a receptacle for storing spermatozoa, a uterus in which the 

 eggs develop, and a vagina by which spermatozoa enter. Self- 

 impregnation is at least a common occurrence. In the ripe 

 joint the distended uterus occupies almost the whole space. 



Some Important Forms. 



Adult or Tapeworm Stage. 



Ttsnia solium^ in man ; the head bears 

 four suckers and many hooks. 



Ttetiia saginata or mediocanellata^ in 

 man ; the head is hookless, with four 

 suckers. 



Tcenzti echinococcus^ in dog. 



Ttsnia cienunts^ in dog. 

 Tcenia serrata, in dog. 



Ttsnia citcumpritta^ in cat. 



BoihriocephalTts latus, in man ; with- 

 out hooks and with two lateral suckers 

 on l^e^d ; the proglottides are less dis- 

 tinctly separate than those of Teenia. 



Bladderworm or Proscolex Stage. 



Cysticercus celluloses, in pig. 

 Bladderworm in ox. 



Eckinococcus veterinorum, with 

 many heads ; in domestic animals, and 

 sometimes in man. 



CtEnurus cerehralis, with many 

 heads, in brain; etc., of sheep. 



Cysticercus insiformis, in rabbit and 

 hare. 



Cysticerc.us/asciolaris, in mouse. 



Embfyo is ciliated and free-swim- 

 ming, becomes a parasite of pike 

 and 'burbot. 



