230 PROGRESS OF MICROSCOPICAL SCIENCE. 



But in all the viperine poisonous snakes which I have examined, a 

 strikingly different arrangement is displayed. Ujion the movable 

 maxillary bone there is room for two poison-fangs, side by side ; and 

 in a macerated skull the tooth in use occupies an extreme position, some- 

 times on one side, sometimes on the other. In sections displaying all 

 the soft part in situ, the remaining space is generally occupied by a 

 tooth which is in process of becoming attached ; and, in whatever part 

 of the area of tooth-development the section be taken, the successional 

 teeth are arranged in pairs, in two parallel series. Thus there will 

 be a right-hand series, consisting of the tooth in i)lace and of four 

 successors, and a left-hand series, consisting of the tooth next about to 

 be in place and four successors. 



When a tooth of the right-hand series has finished its period of 

 work and is about to be shed, it is succeeded by a tooth of the left- 

 hand series, which comes up by its side, and vice versa. A septum of 

 connective tissue separates the two parallel series, and is continued 

 out into the jiouch, which conceals the poison-fangs when at rest, as a 

 free hanging fold : its use appears to be to keep the long axis of the 

 tooth in the right direction prior to its becoming firmly attached, and 

 to jirevent a right-hand tooth from getting into the place of one of the 

 left-hand series, and vice versa. 



It is obvious that this manner of succession is well adapted to avoid 

 loss of time in the changing of the poison-fangs, for much can be done 

 towards the fixation of a new tooth before the old one is detached. 

 That the succession is both rapid and regular would ajipear to be in- 

 dicated by the fact that the successional tooth-sacs are very numerous 

 (often as many as ten), and that they are arranged in jmirs, the two 

 being almost absolutely alike in size and stage of development. Now 

 as any given tooth of the one series is succeeded or preceded by its 

 fellow in the other series, one might expect, if any great interval of 

 time were to elapse, that the one would be materially more advanced 

 than the other. When such is not the case, one is led to the inference 

 that the succession is rapid and also regular. 



In the cobra, the new tooth has to come into place and become 

 attached after the loss of the old one ; and this, it may be inferred, 

 would take much more time. May this not be the explanation of the 

 feat performed by Indian jugglers with the cobra, and their selection 

 of this snake for such purposes ? A cobra disarmed would remain 

 harmless for some considerable period ; a rattlesnake similarly treated 

 would be furnished with a new weapon very sjieedily. 



I have examined specimens in spirit of a few other colubrine 

 snakes ; and although such examinations are less satisfactory than the 

 methods which may be pursued with fresh specimens, I believe it will 

 be found to hold good that in those snakes which have a movable 

 maxilla carrying but one tooth, the successional teeth are developed 

 in two parallel series, this being the highest specialization of the poison 

 apparatus. 



On the other hand, in the colubrine poisonous snakes, approxi- 

 mating more nearly to the harniiess snakes in having a fixed maxilla, 

 Bometimes carrying other teeth in addition to the poison-fang, the 



