200 



L O WER IN VEll TEBRA TES. 



- T(Bma eckinococc 

 and dog. 



found in the intestine of tlie doo 



in front, and the steady enhirgement of those onco formed, until the hindmost ones, 

 being fully matured, drop off the chain. 



Tcenia mediocannellata is distinguished from solium by the want of liooks on the 

 head, and by the fact that the broadest proglottids are those half mature at the middle 

 of the ribbon. The Cysticercus stage is passed in tlie flesh of cattle. 



In Taenia echinococcus the history is reversed, and offers many extraordinary jieeu- 

 liarities besides : reversed because the larval stage infests man and other animals, while 

 the adult is found in one of man's domestic animals, 

 the dog ; peculiar chiefly because one larva produces 

 several adults, and also because the larva differs very 

 much wlien found in man from its form otherwise. 

 The larva in the pig bears tlie name of echinococcus ; 

 it is a large round vesicle usually the size of a walnut, 

 but sometimes growing to be as big as an orange. 

 ITsually it is found in the liver, sometimes in the 

 lungs, and even in other positions. The thin-walled 

 bag has several ingrowths, as shown at A in the 

 accompanying wood-cut, each ingrowth is an in- 

 vaginated head, and becomes a distinct adult indi- 

 vidual. These are everted and broken off, and are 

 shortly after it has eaten the infested flesh of a jiig. 

 The crown of numerous small hooks around the head enables the young worm to 

 anchor itself. It forms only a few proglottids at a time, Fig. B, so that the adult is 

 not more than four millimeters long, the terminal joint soon matures, breaks off, and is 

 replaced. In man, however, the larva is still more complicated, for from the main 

 vesicle grow out secondary sacks, and from the walls of these latter the heads are sus- 

 pended ; the heads thus lie in distinct capsules outside the main vesicle. The illustra- 

 tion, copied from Leuckart, shows the edge of the central 

 sack with one " Brutkapsel " projecting from it. I^he 

 Icelanders are very extensively afflicted by this ]iara- 

 site, and the fact is attributed to their want of cleanli- 

 ness and the ni;mber of dogs that they keep around 

 them. The dogs scatter about the proglottids with 

 their dung, leaving the eggs directly or indirectly u|ion 

 the plants which the Icelanders eat; for they gather 

 for food certain mosses, sorrel, dandelion, and so forth, 

 from the midst of the plains, in which live flocks of 

 sheep guarded l)y dogs. The vesicles are found in all 

 parts of the body, for when the larvaj are set free in the intestine of man they wander 

 about everywhere, until they finally come to rest, and change to the many-headed 

 vesicles. As the vesicles, or hydatids, as they are often called, enlarge, they produce 

 very serious disturbances, and are often fatal. 



Besides the echinococcus, dogs are infested by Tcenia serrafa, which li^-es as the 

 Cysticercus pisiformis in the peritonasum of rabbits and hares, and also by T. cucu- 

 merince. "Some years ago," says van Beneden the elder, "while making a post 

 mortem examination, at the Museum of Paris, of some young dogs which I had pre- 

 viously infected with Tcenia serrata at Louvain, there were found by the side of these 

 some Tcenia ciicumeri?ice. These dogs had taken nothing but milk and Cvsticerci! 



Fig. ISi. —Tainia cchitm- 

 '' Brutkapsel," fro 



L single 



