T^NIASIS 195 



into adjacent tissues and there develop new cysts. This is 

 the limit of their growth, however, in the host of the adult 

 worm. 



Taeniae in Dogs.— The most common taeniae found in the 

 dog are as follows : (a) Dipylidium caninum ( Tarda cucum- 

 erina), a worm 30 to 40 cm. and 3 mm. at its greatest 

 breadth. Its club-shaped head is provided with four 

 suckers and four rows of very small hooks. The neck is 

 long and narrow. The first segments are narrow, the others 

 are longer than they are wide and like melon seeds in form 

 (cucumis). Genital pore double and opening toward the 

 middle of each side of the segments on a slight prominence. 

 Ova are globular, from 37 to 46 microns in diameter, and 

 pass from the segments massed in a small group enclosed by 

 a capsule (cocoon). The cyst form is the Cryptocystis tricho- 

 dectis and the intermediate hosts are the dog flea (Cteno- 

 cephalus canis), dog louse (Trichodectis canis) and the flea 

 that lives on man (Pulex irritans). These intermediate hosts 

 become infested by ingesting the ova of the taeniae which are 

 always present on the skin or hair of the dog by having fecal 

 discharge mixed with the bedding in the kennel. The cysts 

 develop usually in the abdominal cavity of the intermediate 

 hosts which are in turn swallowed by the dog with water and 

 food, or while licking or biting the skin to relieve the irrita- 

 tion which they produce. They then attach themselves to 

 the walls of the intestine where they develop into the adult 

 worm. 



(b) Taenia pisiform is (Tania s errata). — This parasite is 

 about 1 meter long, head a little broader than the neck, and 

 armed with 24 to 38 hooks. Segments at first are much 

 shorter than broad, about square in the middle portion while 

 the mature segments are 10 to 17 mm. long by 4 to 6 mm. 

 broad. Genital pore on the lateral border, and very promi- 

 nent, causing the border to appear convex and the segment 

 to be wider in the middle than at the ends. Posterior borders 

 straight and the angles uneven which gives the strobila a 

 saw-like appearance. Eggs are ovoid and 30 to 40 microns 

 long and 31 to 36 microns broad. The cyst form is the Cys- 

 ticercus pisiformis and is frequent in the peritoneal cavity 



