56 TROPICAL MEDICINE AND HYGIENE 



When these oncospheres are swallowed by a suit- 

 able intermediate host man or sheep in the case of 

 T. echinococciis, or by a lepidopterous insect as in Hymeno- 

 lepis nana, by cattle as in T. saginata, or by pigs as in 

 T. solium the embryonic capsule is dissolved and the 

 embryo with its armed head is set free. It penetrates 

 the intestinal wall, and travelling with the blood-current 

 or otherwise, soon reaches an organ or situation suitable 

 for its further development. The liver, peritoneum, 

 lungs, &c., and muscular system, are favoured places, but 

 no organ, not even the brain, is free from possibility of 

 invasion. 



In such a situation the embryo becomes motionless, 

 and soon globular and cystic, the booklets being spread 

 out over the outer surface of the cyst or dropping off. 

 This the cysticerciis soon becomes a definite cyst, 

 and from the germ cells lining this cyst scolices are 

 produced. In the echinococcus secondary cysts are 

 formed, and in these, the daughter-cysts, scolices may be 

 found. This asexual multiplication may go on indefi- 

 nitely, so that large cystic tumours may be found, as in 

 the well-known hydatid cyst the cysticerciis of T. echino- 

 coccus. From one egg many scolices, and therefore 

 many adults, may result. 



The cysticerci, when ingested by a suitable host, are 

 partially dissolved, the scolices set free, and each scolex 

 may attach itself to the intestinal wall of its new host, and 

 form the head or scolex of an adult tapeworm. The 

 adult cyclophyllidiae differ not only in the structure of the 

 head arid in their development, but also in the arrange- 

 ment of the genital organs present in each segment. 



The opening of the male and female organs is lateral, 

 at the thin margin of the proglottis. The testes are 

 scattered through the parenchyma and the ducts from 

 them lead into a single tube, terminating in a cirrhus 

 pouch at the genital pore. 



Close to this opening is that of the vagina, which at first 

 runs towards the middle line, and then bends laterally, 



