TRANSLATIONS AND SELECTED ARTICLES. 373 



the metamorphoses of the Entozoa and their peregrination through 

 the hving organism. The obvious result of this examination was to 

 excite very weighty doubts in every thoughtful mind. M. Davaine, 

 in his remarkable Traite des Entozoaires, also says that the conclusion 

 in his mind, from the agreement in the facts and the divergence in 

 the opinions of the experimenters, was 'that the question still de- 

 mands sound criticism and fresh researches.' 



" One observer states that, on nine different occasions, he ^as suc- 

 ceeded in producing Taeniae in the intestine of the dog, by causing it 

 to swallow some Caenuri of the sheep. It will be seen that we have 

 also been as successful as this experimenter, and that, in fact, it is the 

 great amount of this success that has given rise to our doubts — we 

 have occasionally reaped more than we have sown. • 



"But before giving an account of our experiments, let us recal 

 briefly what are the Entozoa upon which they have been instituted. 

 The first is the Caenurus cerehralis, a vesicular, polycephalous worm, 

 common in the sheep, in which its presence causes the disease termed 

 ' staggers.' The second is Taenia serrata, a cestoid worm, extremely 

 abundant in the dog. 



" According to the experiments above referred to, this is what takes 

 place : — The dogs devour the heads of the diseased sheep, and the 

 Caenuri are by this means introduced into their stomachs. Having 

 reached this locality, each of the polycephalous helminths separates 

 itself from the parent cyst, elongates enormously, and becomes a 

 Taenia. The entozoon returns to the sheep in this wise : —When the 

 Taeniae of the dog have attained their full development, the rings 

 which they throw off are passed with the excrement, fall upon the 

 grass, and are swallowed by the ruminant. Soon afterwards the ova 

 contained in these segments are hatched in the intestines of the sheep, 

 giving birth to microscopic larvae, which perform what may truly be 

 termed a prodigious journey. From their native seat they force a 

 route into the interior of the head, and, in the course of the journey, 

 are obliged to penetrate through the most varied living tissues — the 

 base of the skull even does not stop them. Instinctively they find 

 one of the openings, and tear through the resisting tissue which fills 

 it up. Having thus finally reached the brain of the sheep, they take 

 up their abode in it, and there produce the Caenurus by which the 

 host will infallibly be destroyed. This closes the cycle of existence 



