288 DB. T. S. COBBOLD ON STRONGYLUS TETEACANTHUS. 



immature worms that I have examined. Figures 10 and 11 were 

 copied from camera sketches. 



It is the question of development that possesses chief interest. 

 As Leuckart has pointed out, the young of this species have been 

 frequently confounded with those of Strongylus armatus ; espe- 

 cially by Colin and Ercolani (quoted below), the latter stating that 

 tbe worm-capsules reach the size of a bean. Eudolphi first fell 

 into this very natural error. In the spring of 1873 I first became 

 practically acquainted with certain small encysted worms that 

 had been removed from the intestinal walls of a pony by Prof. 

 Williams of Edinburgh. The nature of similar finds had for many 

 previous years puzzled both anatomists and helminthologists. In 

 1836 the celebrated Dr. Knox, who had received specimens from 

 Professor Dick, pronounced tbese equine parasites to be " animals 

 similar to Trichina. ^^ The systematist Diesing named the 

 species NematoiAeum Equi Gahalli ; and specimens were subse- 

 quently described by Messrs- Littler and Varnell as " extremely 

 small Ascarides." Like others, I committed errors of interpreta- 

 tion, and (noticing differences of tail-contour which I correctly 

 assumed to have sexual significance) regarded the young para- 

 sites as representing an independent species, which I provisionally 

 named Trichonema arcuata. The error being explained, I yet 

 think that on other grounds it will be convenient to speak of 

 these immature worms as Trichonema-stages of growth, repre- 

 senting one of the biotomes of Strongylus tetracanthus. 



When animals are largely infested by the larvae of 8. tetra- 

 canthus, the young worms first enter the walls of the intestine, 

 and then proceed to encyst themselves in such abundance that 

 throughout a great extent of the colon each square inch of the gut 

 often contains fully one hundred immature Entozoa. In a bad case 

 of infection I counted 39 Trichonemes or young Strongyles within 

 the space of one-fourth of a square inch. In mild cases from two 

 or three to a score may be detected. As obtains in Trichinosis, 

 the amount of infection is a fair criterion of the degree of danger 

 to which the host is exposed. There is, however, this difference, 

 that whereas a fatal result may accrue to the equine host from 

 the presence of a few thousands of young Strongyles within the 

 intestinal walls, a similar disaster to the human bearer requires 

 many millions of Trichinae within the voluntary muscles. Tliis is 

 not an occasion on which to deal with pathological phenomena ; 



