DISEASES OF SHEEP 331 



ILLUSTRATIONS DESCRIBED IN DETAIL. 



Fig. 9. Mature fluke flesh color, one inch to one and one- 

 third inches long- Circle at top is sucker that attaches to diseased 

 part. Mature fluke produces as many as 7,000,000 eggs. Fig. 10 is 

 fluke's egg, oval with transparent shell. An embryo forms in two 

 weeks when temperature is 80 degrees. Fig- 11, egg with embryo 

 formed. Fig. 12, embryo hatched. The broad end is directed for- 

 ward in swimming, in its center is a peg-like projection used in 

 boring. If embryo finds the Limnoeus truncatulus (fig. 13) it com- 

 mences to bore. It bores until it strikes the snail's lung where 

 the embryo fluke develops. The form of embryo changes to fig. 

 14 the 1st generation in the snail termed sporocyst a bag of 

 germs. This sporocyst develops an offspring, their 2nd generation 

 called the redia. Fig. 15 is a matured sporocyst containing a num- 

 ber of redia. The largest one at lower end is well developed and 

 ready to force through the walls of the parent the wound heals 

 up and germs remaining continue to grow. The redia go from 

 the lung to the other organs of the snail. Fig. 16 is a full grown 

 redia with a mouth and intestine and produces the 3rd generation. 

 The offspring of the redia (fig. 17) are tad-pole shaped and called 

 cercaria. This 3rd generation of the snail enters the sheep and 

 produces the liver fluke. The cercaria leaves the snail and becomes 

 attached to and encysted to grass stalks. These cysts remain dor- 

 mant until swallowed by the sheep. The number of cercaria de- 

 scended from a single fluke egg is from 200 to 1,000 or more 

 thus a single fluke may through the changes described above pro- 

 duce more than 100,000,000 descendants in a single season. About 

 six weeks elapse from the swallowing of the tad-pole before the 

 fluke is matured and begins to produce eggs in the liver of the 

 sheep. 



THE SHEEP EOT FLY-OESTRUS OVIS. 



Doubtless most of the diseases of the sheep that are least 

 understood, even by scientific students, at the present time, 

 are those due to the presence of internal parasites, of which there 

 are at least over twenty in number, that are well known and de- 

 scribed. The majority of these are tape worms or thread worms, 

 one only is a fly. We will close the list with the last, as it is 

 well known to all concerned, and the most common of this class 

 of the enemies of the sheep. 



This disagreeable pest is a sort of connecting link between 

 the two classes of parasites, external and internal ones. As a 

 fly, it much resembles a bee, and as it buzzes about the sheeps' 

 heads these animals evince great alarm, lowering their noses to the 

 ground and stamping violently with their fore feet. The fly darts 

 to the sheep's head at every opportunity and deposits an egg 

 on the nostril, while still on the wing. It is the work of an 

 instant, and the mischief is done in the twinkling of an eye. 



The "egg" thus deposited is a living creature, a minute white 

 grub, scarcely differing from that of the common flesh fly which 



