200 AN INTRODUCTION TO ZOOLOGY 



dense fibrous connective tissue. The particular cysticercus of 

 T. solium is called C. cellulosce, and a piece of infected or crysticercoid 

 pork presents a very characteristic appearance, on account of which 

 it is commonly spoken of as " measly pork." 



If pork in this condition is eaten by a human being in a raw or 

 partially cooked condition, for thorough cooking will kill the parasite, 

 the cysticercus becomes set free in the stomach. It evaginates 

 its scolex and throws off its caudal vesicle, and on passing into 

 the intestine attaches itself by means of its head to the mucous 

 membrane. Here the posterior end of the neck starts to grow and 

 segment, giving rise to the long tapeworm with which we started and 

 which is ready to begin the cycle over again. It is obvious from a 

 consideration of its life cycle that improved sanitation and the satis- 

 factory inspection and cooking of pork can keep the parasite down ; 

 indeed in this country it has been practically eliminated, although 

 it is still found in central Europe and may be occasionally introduced 

 here. 



Before passing on to discuss certain general problems 

 connected with the tapeworm, it seems as well briefly to call 

 attention to one or two allied forms that may be encountered and 

 are of interest. 



Tcenia saginata. A form that is also found in man and is on the 

 whole very similar to T. solium, reaching a length of as much as 

 thirty-six metres. It is easily distinguished from that animal by 

 the absence of rostellum and hooks, which are replaced by an addi- 

 tional sucker-like structure, and also by the shape of the ripe uterus. 



f. serrata. This species has been rarely if ever found in man, 

 but is the common tapeworm of the dog. Its cysticercus stage 

 (C. pisiformis), however, is commonly met with in the mesentery 

 of the rabbit and hare, and so encountered in dissecting the former 

 in the laboratory. 



T. echinococcus is a form consisting of but three proglottids at a 

 time, one immature, one mature, and one ripe, and it has a very long 

 rostellum. It makes up for its small size, about 5 mm., by being 

 present in large numbers. It is not found in man save in the 

 cysticercus stage, when man seems to act as an accidental secondary 

 host. The cysticercus, known as C. veterinorum, or in man as 

 G. hominis, produces the condition, sometimes a terrible one, known 

 as Hydatids. The usual place for it is to be found in the liver, where 

 it may reach the size of a child's head, and the one original pro- 

 scolex gives rise by internal budding to thousands of tiny little 

 scolices. 



Dibothriocephalus lotus. As a parasite of man this " broad tape- 

 worm/' growing to a length of nine metres, is more or less confined 



