PROGRESS OF MICROSCOPICAL SCIENCE. 
249 
germs are derived. As they attain considerable length, the forming 
teeth, which were at first vertical, become nearly horizontal, resuming, 
of course, their upright position once more when they come into 
place. The clue to the whole peculiarity of this arrangement is to 
be found in the extreme dilatation which the mouth of the snake 
undergoes. The general capsular investment probably serves to 
preserve the tooth-sacs from displacement ; while, if the forming 
teeth remained vertical after they had attained to any considerable 
length, their points would be protruded through the mucous 
membrane when this was put upon the stretch in the swallowing of 
prey. Just as the author has shown in a previous communication to 
be the case in the Batrachia and Sauria, the hypothetical ' papillary 
stage' is at no time present. From the oral epithelium there 
extends downwards a process which, passing between and winding 
around the older tooth-sacs, after pursuing a tortuous course, reaches 
the farthest and lowest extremity of the area of tooth-development. 
Here its csecal end gives origin to an enamel organ, and, while it does 
so, buds forth again beyond it in the form of a caecal extremity. 
Thus at the bottom of this area of tooth-development there is a per- 
petual formation of fresh enamel organs, beneath which arise 
corresponding dentine organs, or papillae, if such they can be called 
when arising thus far away from the surface. In essential principle, 
therefore, the formation of a tooth-germ is similar to that already 
described in mammals and other reptiles, the difference lying 
principally in the enormous relative length of, and the tortuous 
course pursued by, that inflection of the oral epithelium which serves 
to form the enamel organs. The attachment of the tooth to the jaw 
is effected by the rapid development of a coarse bone, which is not 
derived from the ossification of the feebly expressed tooth-capsule, 
but from tissues altogether external to it. Nevertheless this coarse 
bone of attachment adheres more closely to the tooth than to the rest 
of the jaw, from which, in making sections, it often breaks away. 
The base of the dentinal pulp assists in firmly binding the tooth to 
this new bone, being converted into a layer of irregular dentine. 
This ' bone of attachment ' is almost wholly removed and renewed 
with the change of each tooth." 
Action of Crotalus-jpoison on Microscopic Life. — A most valuable 
paper has been contributed to the Royal Society * by Drs. Brunton and 
Fayrer, on the action of crotalus-poison on animals. We give only 
the author's observations on microscopic life. We also quote Mr. 
Darwin's results, which are of great interest. 
Influence of Cobra-poison on Ciliary Action. 
June 29, 1874. — Ciliated epithelium from the frog's mouth was 
treated with a solution of cobra-poison and examined under the 
microscope. At 1.35 p.m., when examined, the action of the cilia was 
vigorous. At 1.45 it was much diminished. At 1.55 it had entirely 
ceased. Ciliated epithelium placed under microscope ; one part was 
* ' Proceedings of the Royal Society,' No. 159. 
