CH. IX] OF DOMESTIC ANIMALS 311 



beyond the scope of the present work, regarded as un- 

 segmented worms. The " head " is armed with suckers, or 

 hooks, or both appliances, for secure attachment. There 

 is no alimentary canal, but the digested food of the host is 

 absorbed direct through the general surface. Neither are 

 there any special organs of locomotion. The generative 

 organs are of enormous relative proportions, and are present, 

 both male and female, in each joint (proglottis). The 

 sexes, however, are not ripe simultaneously but each 

 proglottis functions first as male and subsequently as 

 female. The prodigious fecundity of these parasites is 

 correlated with the enormous mortality of the embryos. 

 They usually make no effort to find either an intermediate 

 or final host. Success is a mere matter of luck. They 

 are of economic interest inasmuch as not only do they 

 occur as parasites in man, but also, either as bladder-worms, 

 or when mature, in many of our domesticated animals, 

 causing disease of greater or less severity. The species that 

 most commonly come under observation are those that infest 

 the alimentary canal of the dog, and make their presence 

 known by the escape per anum of white flattened, oblong, 

 "joints" (proglottides), possessed of feeble powers of loco- 

 motion. Other symptoms exhibited by the dog are a harsh, 

 staring coat, foul breath and occasional scraping of the 

 rump along the ground. No less than six species of the 

 genus Tcenia are known to occur in the dog, in addition 

 to some three or four species of other genera. The most 

 usual is known as Dipylidium caninum. The eggs of 

 the worm are set free by the decay of the wall of the 

 detached ripe proglottis and are devoured by certain 



