130 



CESTODES. PHYLUM PL ATYHELMINTHES 



by the pig. No further change takes place unless the flesh of a pig 

 infested with such bladder-worms (known as ' measly ' pork) be 

 eaten raw or ' under-done ' by man. When this happens, the 

 stimulus of the new surroundings causes the pouch to be turned 

 inside out. the effective agent being the bile salts (p. 444) acting 

 in a neutral or alkaline medium. This evagination cannot therefore 

 occur until the intestine is reached. The bladder is digested, but 

 the head fixes itself and begins to bud off proglottides. The life- 

 history of Tccnia solium may be summed up as follows : — 



Egg_>.Oncosphere^-Cy sticercus— >-Scolex->Adult . 



It will be seen that only one generation is involved, unless each 

 proglottis be regarded as a complete individual, and not merely 



5 6 7 



^^aO^ 



v\VVV>5 \\f 



•m 



M 







'^v$mmmsM 



m^^ 

 1'. 





Fig. 93. — A transverse section through a proglottis of TcBuia in which the 

 reproductive organs are well developed.— From Shipley and MacBride. 



I, Cuticle : 2, long-necked cells of ectoderm ; 3, longitudinal muscle fibres cut across ; 4, layer of 

 circular muscles ; 5, split in the parenchyma which lodges a calcareous corpuscle ; 6, ovary ; 7, testis 

 with masses of male germ-mother-cells forming spermatozoa ; 8, longitudinal excretory canal ; 

 9, longitudinal nerve cord; 10, uterus ; 11, oviduct. 



as a part of the parent body broken off to carry the eggs. Although 

 the pig is the normal intermediate host, the eggs will develop 

 in man, and heavy human infestations with bladder- worms are 

 known. The adult worm may live in man for more than twenty- 

 five years. 



PLATYHELMINTHES 



The members of the phylum Platyhelminthes are adequately 

 diagnosed as being triploblastic acoelomate Metozoa with no 

 anus. In addition they are bilaterally symmetrical and dorso- 

 ventrally flattened ; they have a flame-cell or protonephridial 

 system (a feature which they share with several other groups) ; 

 and have characteristic complicated reproductive organs. 



