22 



CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE 



grazing. So far as is known, these larvae do not penetrate the skin 

 and must infect horses by being swallowed with grass, water, or dry 

 food which has become contaminated with the larvae. 



The course of development of these parasites after they get into 

 the body of horses has not been definitely ascertained; it is known, 

 however, that not all larvae, and perhaps none of them, go down 

 directly into the cecum and colon and settle there and grow to 



/ 



£<??s reac/ f/?e /pas-ft/re 



w/Y/7 f/?e /va/yar-e &/7<y 



ae^e/op //? a/>a£//aahy/ 



ar fty& t//7c/e/~ /. , , . 



/%r/vre Mtrsns\ / /erz&e W atore/a/? fo 



a/sjpestibe fracfqfMeK /&* '"/ee/'re stipe #>/ 



torse /ay wsTf e#?s. \ ' //? *£*<** »*** *r*o 



{//7a / er/frjscra/>/e cunrffieH&i 



/Verses 6ec&/77<? //7/es/et/ 

 as a re&z//f 0/ * swa/Ap/y/ha' 

 s/7/bc/sire Azrszre /?///? yra&s. 



//7/bcf/fe /ansae -z 

 ' v C///776 a/? /p/srafes 

 ofyrass/h 

 \tyer wearier* 



Figure 14. — Representation of the life history of one of the blood strongyles, & 

 equinus. The illustrations of the adult worms are about natural size and those 

 of the eggs and larvae are enlarged about 75 times. This illustration is typical 

 of the life cycle of horse strongyles generally. 



maturity. On the contrary, the larvae, after entering the body of 

 the horse, undergo extensive migrations which bring them to various 

 organs and tissues, such as the liver, pancreas, spleen, lungs, kidneys, 

 and other organs and tissues, from which many of the larvae probably 

 fail to get back to the large gut. However, those larvae which return 

 to this organ become attached to its wall and develop to fertile 

 maturity. The eggs which are produced by the female worms and 

 eliminated from the horse's gut with the manure start the cycle of 

 development once more. 



