198 THE GROUSE IN HEALTH AND IN DISEASE 



although one end of the fork of the now Y-shaped worm dwindled and 

 came to nothing, the other was already shedding mature " proglottides " 

 or " segments " crowded with eggs. 



The large tapeworm occurs only in the small intestine of the Grouse. 

 Sometimes the number of specimens is small, two or three ; at other 

 times and this is especially the case with weakly and diseased birds 

 the number of worms amounts to dozens, and they so fill the lumen 

 of the alimentary canal that it seems difficult to imagine how the food 

 can squeeze past them. In a badly infected bird worms of very different 

 sizes are met with. 



The anatomy of this form has been fully described in the Official 

 Report : here we need only consider a few facts of more general interest. 



Both the " rostellum," or protrusi- 

 ble anterior end of the head, and the 

 four suckers are armed with hooks. 

 We shall consider later how far these 

 hooks can act as inoculating agents. 

 The number of proglottides or seg- 

 ments varies with the size of the 

 worm. The medium-sized speci- 

 mens possess some two hundred 

 and fifty proglottides the long 

 worms may have four hundred (see 

 Fig .16). The posterior proglottides 

 are continually breaking off, singly 

 or in short chains of two or three, 

 and, leaving the intestine of the 

 Grouse with the dejecta, they come 

 to He about on the moors. Each 

 proglottis contains, at a very rough 

 estimate, some two hundred eggs, 

 so that at any given moment a 

 D. urogalli would contain nearly 

 one hundred thousand eggs. But 

 this is no measure of the fecundity 

 of the tape-worm, because as fast as the proglottides break off at the 

 tail end new ones are formed at the head end, and the animal goes on 

 and on producing new proglottides like a recurring decimal. The ova 

 are excessively small, and they must be disseminated in millions all 

 over the moors. As already explained, they probably make their way 

 into some insect spider or mollusc, and there turning into the cystic or 

 larval stage await the moment when the insect is swallowed by a 

 Grouse to assume again the adult characters. An enormous number 

 of the eggs must perish without ever meeting with those conditions 

 which alone permit them to develop. 



FIG. 16. Davainea uro<j<illi. 



