20 . Circular 338, 11. S. Department of Agriculture 



cutting plates (fig. 19), but is without the six teeth which are 

 present in the common dog hookworm. It is, however, a blood- 

 sucker like the other. 



The female w^orms produce numerous eggs (fig. 20) which pass 

 out in the feces and under favorable conditions ma}^ develop in the 

 course of 36 hours to the stage where each egg contains an active 



Fig. 19. — The narrow-headed dog hookworm, Uncinaria stenocephala. Head. Left, dorsal 

 view ; right, lateral view. Enlarged. From Riley and Fitch, after Looss 



embryo. In the course of from three to six days, as a rule, a first- 

 stage larva hatches from the egg. In about three more days this 

 larva molts its skin and forms a second-stage larva. In about 

 eight more days this larva molts to form a third-stage larva which 

 retains the skin of the previous stage for a time at least. This is the 

 infective larva, capable of infecting dogs when swallowed in con- 



Fio. 20. — Eggs of commop. dog hookworm. EiiLirgod. From Railliet, 180."^ 



taminated food or water, or when put in contact with the feet or any 

 part of the dog's skin. Whether the larvae enter by the mouth or 

 through the skin, they go into the circulation and behave in much 

 the same w^ay that the ascarid larvae behave, ultimately getting to 

 the lungs, entering the air passages, going up these to the- mouth, 

 being swallowed, and finally reaching the smiill intestine, where they 

 undergo two more molts and then become mature worms. Eggs from 

 these worms usually appear in the feces in four or five weeks after in- 



