CH. IX] OF DOMESTIC ANIMALS 313 



Fig. 53. Tania solium. Slightly magnified. 



A. Entire worm showing head and proglottides. 1. Sucker on head. 

 2. Genital pores. 3. Ripe proglottis. 



B. Head. 1. Kostellum. 2. Hooks. 3. Suckers. 4. Neck. 

 5. Commencement of strobilization. 



C. Eipe proglottis broken off from worm. 2. Eemains of vas deferens 

 and oviduct. 3. Branched uterus crowded with eggs. 



external parasites of the dog, such as the flea (Pulex 

 serraticeps) and louse (Trichodectes latus), and give rise 

 to the bladder-worm in these intermediate hosts. Beyond 

 this stage it does not progress except it be devoured by 

 dog, fox, wolf, etc. ; in which event the bladder disappears 

 and the " head " of the worm attaching itself to the lining 

 of the intestine of the new host buds off a long series of 

 "joints," each of which in due course after sexual maturity 

 becomes crowded with fertile eggs. The success of this 

 parasite then depends upon the dog nibbling and biting 

 at the fleas or lice which are irritating him, especially 

 when these happen to be in the region of the anus, and 

 the hair of the dog matted with faeces. 



In dissecting a rabbit one may often meet with small 

 bladder-worms attached singly or in clusters to the 

 mesentery ; this form is known as Cysticercus pisiformis, 

 and is, as its name indicates, about the size of a pea : it 

 gives rise in the dog to the tape-worm Tcenia serrata. 

 The cystic stage of Tcenia ccenurus, another species found 

 in the dog, is Ccenurus cerebralis, which occurs in the 

 brain and spinal cord of sheep and horses and causes the 

 complaint know as "gid" or "staggers." This bladder- 

 worm may be as large as a walnut and contains numerous 

 " heads " each capable of producing a complete tapeworm. 



