REPORT OF THE SOCIETY 103 



cat. The white mouse, which you see (fig. 3), is a laboratory reared one 

 which accidently picked up apparently a whole segment of the mature 

 tapeworm. Instead of developing the one to three or four, or a limited num- 

 ber of cysts, which we ordinarily find, it developed the myriad represented 

 by the little rounded areas and the result was fatal. 



Just as one of the commonest tapeworms of cats is the species which 

 passes its immature stage in the mouse or rat, so the commonest one of 

 hunting dogs is a species. Taenia serrata, which develops its cystic stage in 

 the rabbit. Eggs which are scattered by infested dogs on herbage are swal- 

 lowed by rabbits, and develop as cysts in the body cavity of these animals 

 (fig. 4). The infested rabbit, or its viscera, are eaten by dogs and the mature 

 worm develops in them. They in turn pass the ripe segments (fig. 6), and 

 eggs are scattered to be taken up by rabbits. Thus the cycle continues in 

 nature. 



I was careful to refer to this last species as one of the commonest tape- 

 worms of hunting dogs. Still more common in pet dogs and in cats is the so- 

 called double-pored tapeworm, Dipylidium caninum (often referred to in 

 medical literature as Taenia cucumerina). The reason for its occurrence 

 in these animals is understood when we learn that this worm has as its 

 intermediate host the dog louse or the dog flea. In these insects, whose larvae 

 have fed upon eggs from the infested dog, the minute larval tapeworm de- 

 velops. So minute are these that as many as fifty have been found in a 

 single dog. Rather rarely this tapeworm has also been found in humans. 

 When we consider that it can only develop in one who has swallowed the 

 intermediate host of the worm, it is not surprising that most of such cases 

 have been of children. A possible method of infection is illustrated by fig. 7, 

 a photograph whose charm is lost when we consider it from the viewpoint of 

 parasitology. 



Another instance of insects serving as intermediate hosts of a tapeworm 

 of man is afforded by Hymenolepis diminuta. This ordinarily occurs in its 

 sexual stage in rats and mice. The eggs are dropped by these hosts and 

 develop the asexual stage in various grain-infesting insects. These taken up 

 by rats and mice pass on the infestation. Man becomes infested by ingesting 

 the Insect-host in imperfectly cooked cereals and similar foods. 



The best known of the tapeworms of man is Taenia saginala, which 

 may attain a length of thirty-five to forty feet. It has been estimated that a 

 single one of these worms may produce 150,000,000 eggs within a year. 

 These, when taken up by cattle, develop into the cystic form. Man becomes 

 infested by eating raw or imperfectly cooked beef containing these cysts. 

 These develop into the sexually mature worm in from two to three months. 



