112 THE INTERNAL PARASITES OP 



invade the kidney, the bronchi, and the large in- 

 testine. 



Several larval nematodes have also been described, but 

 their precise genetic relations are at present only 

 imperfectly known. 



It will naturally be expected that I should say some- 

 thing more respecting the habits and development of the 

 palisade worm (Strongylus armatus). This is the 

 entozoon which produces the so-called worm aneurism 

 in the horse, and still more frequently in the ass. 



Its natural history has long remained a puzzle to 

 veterinarians, and even now all the phases of its life-cycle 

 are not perfectly understood by the helminthologist. We 

 know enough, however, to enable us to correct many 

 errors currently entertained, and also sufficient to guide 

 us towards a correct interpretation of the stranger phe- 

 nomena associated with the wanderings of this interesting 

 nematode. Thus, the worm as it is commonly found in 

 the blood vessels is constantly spoken of as a variety of 

 the species in question, whereas the Strongylus armatus 

 minor, as it is termed, is only the same parasite in a 

 sexually immature condition. The illustration (Fig. 26) 

 represents a number of these worms lodged in the 

 mesenteric artery of an ass. 



What we know of the development of this parasite 

 is chiefly due to the researches of Professor Rudolf 

 Leuckart. 



As obtains in the case of one of the sheep's strongles 

 (8. hypostomus), it appears that the embryos are not 

 developed within their eggs until the latter have been 

 expelled and lodged within moist mud. Here the so- 

 called rhabdifciform young, or larvge, will change their first 

 skin in about three weeks, and at the same time part with 



