56 ESSENTIALS OF ZOOLOGY 



introduced, it is believed, by cross -fertilisation when possible 

 into the oviduct, which thus acts as a vagina and spermatheca. 

 The eggs are fertilised, and together with a quantity of yolk 

 are covered by a shell. The eggs as they are completed are 

 passed into the uterus. The uterus thus becomes greatly dis- 

 tended, and as it becomes filled with eggs it gradually occupies 

 a great part of the space available in the segment, and the 

 other reproductive organs become correspondingly reduced. 



In the uterus the eggs undergo their early development, 

 an embryo being formed provided with six hooks and called 

 the hexacanth. 



The detached proglottides passed out from the dog in the 

 faeces are scattered about on pastures, and, if the intermediate 

 hosts do not become infected with them immediately, the 

 proglottides gradually decay and the eggs are liable to further 

 dispersion. When the eggs are eaten the coat surrounding 

 them is digested in the stomach of the rabbit and the hexa- 

 eanth liberated. The hexacanths obtain entrance to the 

 blood by burrowing through the wall of the stomach or 

 intestine and are conveyed by the portal circulation to 

 the liver. Their presence in the liver is marked as early 

 as the second day by small white nodules formed in the liver 

 of the rabbit in response to the irritation produced. The 

 further progress in growth is traceable by haemorrhagic 

 streaks, which become sinuous and increase in size, either in 

 or on the surface of the liver. These contain the cysticerci 

 more or less surrounded by coagulated blood. The interlobular 

 blood-vessels containing the cysticerci become obliterated, 

 and the cysticerci are enclosed in a sheath formed around 

 them by the leucocytes of the blood. The cystic ercus at 

 this stage is an elongated vermiform body. It consists of a 

 thick-walled sac invaginated at one end, and the cup has pro- 

 jecting into it a scolex. It is probable that it multiplies by 

 transverse fission. In about a month the cysticercus is in a 

 condition to quit the liver. It enters the peritoneal cavity 

 and again becomes encysted, singly, or in clusters, around the 

 stomach or in other parts of the peritoneal cavity. It cannot 

 undergo further development unless it is eaten by the dog. 



