238 ZOOLOGY. 



fact that the bladder-worm lives in the brain of young 

 sheep. If a sheep-dog harbours Tcenia ccenurus in 

 its stomach, a sheep may very easily take up a joint 

 with grass or heath. The joint is then digested in the 

 sheep's intestine, and the larva escapes from the egg. 

 It bores through the wall of the sheep's intestine, gets 

 into the circulation, and is carried by the blood-stream 

 to various parts of the body; it can only develop 

 further, however, in the brain (or spinal cord). After 

 the minute larvae have reached the cavity of the 

 cranium they move about on the outer surface of the 

 brain, and dig out channels there till they find a 

 suitable place for further growth. The larva now 

 becomes a bladder- worm, which gradually grows, until 

 it attains a size varying from that of a nut to that of 

 a hen's egg. It develops numerous tapeworm heads, 

 even from three to four hundred. These become tape- 

 worms if a sheep is killed by the parasite, and its 

 head devoured by a dog or fox. 



The disease caused by the presence of bladder- worms 

 in the brain is called " gid," or " sturdy," also 

 "staggers." Two stages can be distinguished in it. 

 During the first period the symptoms of disease are 

 chiefly due to the wounds which the larvae make on 

 the surface of the brain, and the consequent inflamma- 

 tion of the investing membranes. Even in this stage 

 the disease may be fatal, but the symptoms cease as 

 soon as the larvae cease to move about. The bladder- 

 worms are only able to do harm by the pressure they 

 exert, which is small at first, though it gradually 

 becomes greater. The first stage of gid manifests 

 itself in late summer, the second in late autumn, 

 winter, or spring, according to the rate at which the 

 bladder-worms develop. The symptoms of the first 

 stage are caused by the increased flow of blood to the 

 brain and head generally, resulting from the irritation 

 which the larvae exert. (Head very hot. Eyes blood- 

 shot. The sheep are sluggish but restless, and carry 



