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 (Tenia perfoliata Goeze). 
This is a small species, seldom becoming more than three 
inches long and a third of aninch 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 
ccecum 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 larve 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 (7. 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 Tenia perfoliata, natural size. From Cuvier. 
Figure 72.—Head of 7. plipiiané maar rom Cuvier. 
