ASOARIS MYSTAX. 331 



Trichocephalus has been well investigated, more particularly by- 

 Mayer, Siebold, Dujardin, Blanchard, Kiictienmeister, and Eberth ; 

 but (as I have shown in my third memoir on " Entozoa," published 

 in the " Linnean Society's Transactions ") the statement of Kiichen- 

 meister, that there are no external appendages in the female of 

 Trichocephalus comparable to those known to exist in the allied 

 Trichosomata, is incorrect. In connection with these organs I have 

 also endeavoured to throw light upon the conflicting statements of 

 Mayer and Eberth, and I have demonstrated, more fully, the very 

 marked differences existing between the males of Trichocephalus 

 affinis and T. dispar. The presence of the last-named species in 

 the human body is fortunately attended with very little incon- 

 venience ; but its development and mode of gaining access to the 

 host has, nevertheless, been recently made the subject of diligent 

 inquiry. Leuckart's, and especially also Yirchow's, researches 

 have entirely disproved Kiichenmeister's notion that Trichince are 

 the young of Trichocephalus; and the experiments of Davaine 

 render it probable that the young get into the human body in a 

 manner very similar to those of Ascaris lumbricoides. The latter 

 authority finds that the eggs undergo no development whilst yet 

 lodged within the host's intestine, and they are expelled per anum 

 in the immature condition in which they make their escape fi"om 

 the body of the parent worm. It further appears that, after their 

 expulsion, a period of six months must elapse before the embryonic 

 formation commences — an interesting circumstance, and one which 

 satisfactorily explains why it was that my own feeding-experiments 

 (on a chicken and rabbit) with the fresh eggs of Trichocephalus 

 affinis gave only negative results. According to Davaine, the fully 

 developed embryo measures ^ of an inch in length, and, inas- 

 much as it tapers gradually from behind forwards, to a certain 

 extent, resembles the parent. 



For other anatomical details and illustrations of Trichocephalus 

 I must refer the reader to the fifth chapter of the first part of this 

 work. 



