POISONOUS SXAKES OF NORTH AMERICA. 



383 



which is as yet incomplete and but little more than lialf what it ulti- 

 mately becomes. There are now scales on the tail, but tliey show no 

 fusion with the button around its front border. Within the button the 

 vertebra! are still distinct and surrounded by muscle. The next step 

 is illustrated by one-week-old young ones of the same species (figs. 28, 20), 

 S^ inches in length, which show a decided gain, the externally visible 



Fig-. 28. 



TAIL END OF ONE-WEEK-OI,D MASSASAUGA. 



Side view. Nearly three times natural size. 



( After Garman. ) 



Fig. 21). 



DIAGRAMMATIC LONGITUDINAL SECTION OK FIG. 28 



part of each ring having been now acquired. In no case is there any 

 disposition on the part of the scales to fuse with the button. Inside 

 of the latter the changes have been even greater; the vertebra, still 

 plainly outlined, have consolidated into a single elongate mass, the 

 size of which is being increased by both lateral and terminal growth; 

 the vertical processes have grown together; and the muscles have been 

 displaced by the enlarging bone and the thickening skin. Figs. 30 

 and 31 iinally show ns the status of a 14-inch-long Prairie Rattlesnake, 



Fig. 30. 

 INCIPIENT HATTLE OF YOUN(; PUAIKIE RATTLE- 

 SNAKE. 



Side view. IJ natural size. 



(After Garman ) 



Fig. 31. 



DIAGRAMJLATIC LONGITUDINAL SECTION THROUGH 

 FIG. 30. 



Crotalus conjiuentus, which was taken, with the third button about 

 half grown, when the process of pushing back the second ring was 

 well under way. The first ring had been set free with the first shmgh, 

 holding only by the collar, and if the snake had been allowed to live a 

 little longer, the second sloughing would have discovered the third 

 button perfected, clasped by the second ring, the latter pushed back 

 and loosened from the balance of the epidermis. 



It should be added tliat the ])eriod of appearance of the first joints 

 seems to vary, inasmucli as there are apparently trustworthy recm-ds of 

 embryos having been found witli more than one joint.* It is interest- 

 ing, in this connection,to remember Dr. Hay's observation that hognose 

 snakes commenced to shed their skin witliin a few minutes after having 

 left the egg.t As the young Eattlesnake leaves the eg^ covering before 

 being born, may it not also occur that it sheds its skin before birth— 

 at least, sometimes ? 



'Hopley, Snakes, 1882, p. 299. 



tProc. U. S. Nat. Mus., xv, 1892, p. 394. 



