376 



PARASITES OF ANIMALS 



rest of the body, being of a slender cylindrical form with a 

 rounded-off extremity. The development of the sexual apparatus 

 had not yet commenced. Notwithstanding the great differences 

 of size presented by the body, the structure of all examples was 

 exactly the same to the minutest particular, without exception. 

 Also the smallest specimens, which scarcely measured one milli- 

 metre, found in capsules of 0*3 mm. in diameter, were distinguish- 

 able only by the absence of the oral cup, whose position was 

 represented by a slender and thickened chitinous cylinder, as 

 obtains in the earliest parasitic juvenile condition of Dochmius 

 trigonocephalus. The transformation to the form presenting an 

 oral cup occurs through a moulting, which is accomplished 

 already in examples of 1'5 mm. in diameter. Later, also, the 

 worms cast their skins in their capsules, without, however, 

 changing the oral cup. In regard to the final purpose of this 

 metamorphosis, my investigations have left me entirely in the 

 lurch ; nevertheless, I do not entertain the smallest doubt that 

 the worms which I have here described are the larval forms of 

 Strongylus tetr acanthus." 



From numerous examinations I have satisfied myself that 

 the worms after escaping the walls of the intestine and 

 they may often be observed in the very act of passing 

 re-enter the lumen of the bowel to undergo another change 

 of skin prior to acquiring the adult state. This they accom- 

 plish by rolling themselves within the faecal matter of the 

 horse's intestine. The best examples I have seen of this 

 phenomenon occurred in a case for the clinical particulars of 

 which I am indebted to Mr Cawthron. 

 Most interesting was it to notice these 

 immature worms, each coiled within a 

 sort of cocoon, which Mr Cawthron 

 termed a cyst. All the forty little 

 cocoons more or less resembled pills, 

 the bright red color of their contained 

 worms strongly contrasting with the 



FIG. 64.-F^n y sts or pellets con- dark color of the cocoons. They con- 

 sisted of compressed debris, which under 

 the microscope showed many common 

 forms of vegetable hairs and paren- 

 chyma, besides raphides and chlorophyll-granules. Internally, 

 there was a cavity corresponding with the shape of the worm. 

 In one instance I noticed that the worm had nearly completed 





