PARASITES OF ANIMALS. 99 



Britain, with a high tax on dogs, there is only one to fifty. 

 Doctor Krabbe found the echinococcus tape-worms in twenty- 

 eight out of one hundred Icelandic dogs examined, while in 

 Denmark he found them in less than one per cent, of the 

 three hundred and seventeen dogs examined for this purpose. 



Tape-worm of the Horse ( Tcenia perfoliata Goeze). 



This is a small species, seldom becoming more than three 

 inches long and a third of an inch broad. The head is rather 

 square, with four prominent suckers, but without a proboscis 

 and hooks. There is no distinct neck, the first joints behind 



Figure 71. Figure 72. 



the head being broad, but short. There are about 45 joints 

 in full-grown specimens. The reproductive organs open on 

 one edge of the joints, the first 22 segments having both male 

 and female organs, the rest only female. 



It occurs quite frequently, in considerable numbers, in the 

 coecum and colon of the horse, and more rarely in the small 

 intestine. The development and the source from which 

 horses derive them are unknown. The larvae may, perhaps, 

 live in insects accidentally swallowed with grass. It does not 

 appear to produce any serious disease, unless in great num- 

 bers, and may be expelled by the same medicines used against 

 the human tape-worms. 



A still smaller species, T. mamillana Mehlis, only about 

 half an inch long, and also without a distinct neck, but with 

 wedge-shaped joints, lives in the large intestine of the horse. 

 A much larger species than either of these (T. plicata Rud.) 

 lives in the small intestine and sometimes in the stomach of 

 the horse. It grows to the length of three feet or more, and 

 has a remarkably large head, with four suckers, but no hooks 



Figure 71. Young Tcenia perfoliata, natural size. From Cuvier. 

 Figure 72. Head of T . perfoliata, magnified. From Cuvier. 



