178 PARASITES OF THE DOMESTIC ANIMALS 



rare in aged sheep. Where fatahties occur, they are usually among the 

 grazing lambs. 



Cestodes op the Dog 



Of the tapewoi'ms of the dog, nine are considered here, among which 

 there is a wide variation as to frequency and importance. The first 

 eight of the species to be mentioned belong with the family Taeniidse; 

 the ninth is referred to under the Diphyllobothriidae. In all but the 

 last the head is provided with the crown of hooks, and in all the life 

 history is known. 



1. Dipylidium caninum (Taenia cucumerina). Fig. 94. Taeniidae 

 (p. 170). — The head is small and has a protractile rostellum surrounded 

 by the four suckers (Fig. 95). There are three to four rows of small 

 thorn-like hooks. The neck is slender, succeeded at first by narrow 

 trapezoidal segments. The nature segments are longer than wide and 

 shaped somewhat like a cucumber seed. They have a genital pore on 

 each lateral margin. 



Length, 15-40 cm. (6-16 inches). 



Eggs globular, 43-50 microns in diameter and grouped in small cap- 

 sules (Fig. 96). 



The larva of this worm is a cysticercoid {Cryptocystis trichodectes) 

 found in the body-cavity of the biting louse of the dog, — Trichodectes 

 latus (Fig. 96) . Lice are not sufficiently prevalent upon dogs, however, 

 to account for the frequent occurrence of this worm; in fact, later in- 

 vestigations have determined that the dog flea, Ctenocephalus canis, 

 and the human flea, Pulex irritans, harbor its larva, and it is probable 

 that the flea is its more common host. 



2. Dipylidium sexcoronatum. Tseniidae (p. 170). — Hall and Wigdor 

 (Journal of the American Veterinary Medical Association, June, 1918) 

 refer to this tapeworm as follows: "Dipylidium sexcoronatum has been 

 reported from dogs in the United States at Bethesda, Md., and Detroit, 

 Mich., by Hall (1917). We find it fairly often here at Detroit and our 

 impression is that it is as common here as D. caninum. The strobila is 

 much narrower than D. caninum. Some of the specimens with a narrow 

 strobila appear to have only five rows of hooks and should be studied 

 with a view to determining whether D. sexcoronatum has sometimes five 

 rows of hooks, as well as six rows, or whether this material belongs to a 

 new species." 



3. Taenia hydatigena (T. marginata). Fig. 97, Taeniids (p. 170). — 

 The head is small, but little broader than the neck. The hooks are 

 large, 170-220 microns long, and number 30-34. The mature segments 

 are wider than long, the distal segments elongated. The gravid seg- 

 ments have a median longitudinal groove terminating in a notch pos- 



