DE. T. S. COBBOLD ON 8TR0NGTLTJS TETRACANTHIJS. 289 



but as illustrating one step in the migratory process, I may 

 mention that many of the larger and more superficially placed 

 cysts display lesions of their walls, the young worms already 

 protruding their heads. In short, I have taken tliem, as it were, 

 in the very act of immigrating to the lumen of the intestine 

 whence they had originally emigrated. Without detailing the 

 pathological processes thus set up, it is sufficient to say that they 

 aflford irrefragable proofs of the dangerous character of this 

 entozoon. 



In any portion of a much-infested intestine it is usual to 

 observe variations in the size of the cysts, each of which contains 

 a single worm. As in some cases the sizes form natural groups, 

 it is clear that the equine host may be infested by successive 

 broods. Variations of structure are seen in the growing larvse, 

 but in the earliest encysted stage a well-formed intestine is 

 invariably present. One of the smallest worms that I measured 

 was only jtj of an inch in length by y-^fj-" in breadth. In the 

 advanced stage, in which condition the worm is about to re-enter 

 the lumen of the host's intestine, one observes a distinct oral 

 ring, a funnel-shaped buccal cup, a muscular oesophagus with 

 the usual chitinous cylinder, and a strongly pronounced mid gut, 

 presenting constrictions throughout the chylous portion and 

 everywhere walled-in by large nucleated cells that are most con- 

 spicuous towards the rectum. Although thus far no structural 

 differentiations mark the presence of internal sexual organs, 

 the sharp-pointed tails of some of the worms and the short 

 conical tail of others already point to differences of sex. The 

 immature character of the worms was recognized by me from 

 the first, but, as already implied, I was unable at the time to 

 refer them to any of the hitherto known species*. 



In Helminthology one must always be prepared for surprises. 



* In 1831 Gurlt had recognized the cii'cnmstance that " die jungen Wiirmer 

 liegen zusammengekrummt in der Substanz der Schleimhaut, wo sie wie 

 scharze Puntte erscheinen." He spoke of two varieties of the sexual worm, 

 and remarks: — "Auch die kleinere Varietat findet man in der Begattung." 

 The largest of my so-called Trichonemes correspond in size with Gurlt's smaller 

 variety of the adult worm, but as I never saw them in the condition he de- 

 scribed they can hardly be the same. Dr. Krabbe's description of the cyst is 

 similar to that of Gurlt, but he makes no mention of the helminthiasis thus 

 produced. [For references, see Literature quoted below. — T. 3. C] 



