therefore, if the fangs failed to engage, they would penetrate the lower jaw. But there is a certain movement among the loose bones of the skull (perhaps not yet thoroughly made out), the result of which is to spread the points of the fangs apart, so that they clear the inner sides of the under jaw, instead of injuring them.’ Coues here describes rattlesnakes particularly, but no doubt the same extends throughout the viperines.... ‘In a large snake the entire gland may be an inch long and one-fourth as wide, having the capacity of ten or fifteen drops of fluid. There is no special reservoir for the venom other than the central cavity of the gland. Formerly there was thought to be such a storehouse; but when the tooth is folded back, certain muscles press or compress the canal to prevent a wasteful flow: in other words, the communication is shut off!’ In this wonderful exhibition of the ivory hypodermic syringe there has not, I trust, been so much repetition as to render the subject tedious. Presented in such graphic language and from such a source, it must attract almost every intelligent reader, while the viperine fang is absolutely acting before his eyes. On this subject, then, no more need be said; though on the Crotalus family generally some interesting matter still remains to be told. [Illustration] CHAPTER XXI. _THE CROTALIDÆ._ IN the several chapters in which the rattlesnake has been introduced, the reader has seen that for about 250 years it has been an object of interest and of study among naturalists, and that first one and then another has made fresh examinations of its various parts, giving to the world new items of information as the results of such observations. And can there remain anything further to find out about it? we may ask in surprise. Yes, there is. There yet remains to comprehend and decide upon one feature which thus far has defeated conjecture and investigation—the ‘pit’ (p. 277). Possibly among the indefatigable observers in the land of rattlesnakes, recent labours may have been rewarded by some new evidence of the utility of this peculiar orifice, and already their zoological journals may have enlightened ophiologists on its functions. At the present moment I am not aware of such information; and time will not permit of further delay to enable me to send a message of inquiry across the great deep. Hitherto the pit has certainly plagued not only zoologists, but all classifiers of the Ophidia; because serpents that have this facial depression embrace so many widely differing genera, some of them resembling in all other respects the true vipers, and others the rattlesnakes, so that they have come to be distinguished as the ‘pit vipers.’