DEVELOPMENT AND METAMORPHOSES OF TiENI/E. 651 
salmon, trout, axolotl, frog, and lizard—that the nervus 
olfactorius is the first part to be developed ; that it arises at the 
same time as the other cranial nerves, and in the same man¬ 
ner; that it appears before the cerebral hemispheres, and 
consequently arises from the original fore-brain. He finds, 
further, that there is no trace whatever of an olfactory vesicle 
in the chick till the end of the seventh day, or in the dog-fish 
till stage O of Balfour’s nomenclature; in the salmon and 
trout there is no trace of an olfactory vesicle up to the time of 
hatching, nor, indeed, for some time afterwards. 
Dr. Marshall maintains that the olfactory vesicle must, 
therefore, be regarded as a structure of merely secondary im¬ 
portance ; and that the olfactory nerves, since in their early 
stage they do not differ embryologically in any respect from 
the segmental cranial nerves, must be regarded as the first or 
most anterior pair of true segmental nerves. 
DEVELOPMENT AND METAMORPHOSES OF ThENLE. 
Thirty years ago Van Beneden, Siebold, Leuckart, and 
Kuchenmeister established, by experiments on carnivorous 
animals, not only that the vesicular worms were imperfect 
forms of Taeniae, but that it was indispensable that the worms 
should be swallowed by an animal to bring them to the 
perfect state. 
This view, while explaining the origin of the armed 
Taeniae of carnivorous and some omnivorous animals, did 
not, however, explain that of the unarmed Taeniae of herbi¬ 
vorous animals. The horse, ox, sheep, &c., often have adult 
Taeniae, and yet they do not swallow any organism capable 
of harbouring the scolecides of their Taeniae. 
M. P. M6gnin thinks* he has discovered the key to the 
enigma from an examination he made of some horses and 
rabbits. In these animals, the Echinococci and Cysticerci, 
when they develop in the adventitious cavities in immediate 
communication with the interior of the intestine (cavities 
resulting from the enlargement of follicles or glandules into 
which the hexacanthian embryos have introduced them¬ 
selves), or even when they become free in the peritoneal 
cavity of the wild rabbit, continue their metamorphoses on 
the spot, and arrive at the adult state without quitting the 
organism into which they penetrated as a microscopic egg 
(•03 to *07 mm. in diameter) either with the food or drink of 
* ‘Comptes Rendus, 5 vol. lxxxviii (1879), p. SS. 
