ANIMAL PAEASITES. 27 



in the interior of their caudal vesicle, in order to their develop- 

 ment, would be inconceivable, if they had to collect the nutritive 

 fluid for themselves, and did not contain it in them. 



9. Dropsy in its nature is an anomaly of secretion and excre- 

 tion ; the cysticercal vesicle is the product of resorption. 



10. We introduce artificial separations where science must and 

 will unite, and thus disturb our comprehension of the process of 

 development in the Tanice. 



11. The cystic worms are not strayed dropsical tape-worm 

 nurses, but tape- worm larvae furnished with a provisional organ 

 (caudal vesicle), probably acting as a reservoir of nourishment, 

 and incapable of sexual multiplication, for which there is neither 

 room nor sufficient nutritive material. 



12. The cystic worms constitute a necessary step in the develop- 

 ment of the T&nite. 



13. We cannot speak of dropsy or degeneration (for, as I 

 afterwards pointed out, we can only speak of degeneration, and 

 I might add of disease, when we are acquainted with the different 

 normal or healthy states), and not even of straying, because we 

 do not yet clearly perceive how the blood could get to the 

 dwelling-place of the cystic worm. (Leuckart has recently put 

 forward the opinion with regard to the straying hypothesis, that 

 in this case we must also regard the young brood of a frog, in a 

 pond which is drying up, as strayed.) 



At the same time, I proved that the Cysticerci adminis- 

 tered, when transferred to the intestines of other animals (as, 

 for instance, the Cysticercus pisiformis in the intestine of the 

 cat, &c.), did not become developed into jointed tape-worms, 

 but bore behind the head a long, inarticulated appendage, 

 and died in a short time, without being any further developed ; 

 and that every species only thrives in a particular species of 

 animal. 



In the course of the year 1852 Von Siebold had repeated these 

 experiments, partly himself and partly by his pupil Lewald ; and 

 was thus, as he said, convinced of the possibility of the conversion 

 of the cystic worms into T&nice. In the first supplement, 

 No. 200, of the ' Breslauer Zeitung/ of the year 1852, he reported 

 upon the experiments proving this metamorphosis with Cysticercus 

 pisiformis, C. fasciolaris, and Cosnurus ; and upon the commence- 

 ment of experiments with Echinococcus veterinorum, and by 

 Lewald, in his dissertation ' De Cystiscercorum in Tsenias 



