1893.] NEW-YORK MICROSCOPICAL SOCIETY. 63 



stances, I gave an account of it to the American Naturalist, Janu- 

 ary, 1875, and also in Nature, November, 1879. The serpent, in 

 fact, is the only creature that can denude itself with the peculiar 

 results which have just been mentioned. The anatomy and phy- 

 siology of the animal are singularly fitted for the operation. The 

 ophidian eye is immobile. Though the books speak of the ser- 

 pent's eyelids, it is simply accommodating language, for it has no 

 true eyelid. Citing P. Martin Duncan in substance, the so-called 

 eyelid of the serpent is an immovable covering of three superposed 

 layers. First, there is the outer one, the epiderm, which is moulted; 

 this is elastic, and is the thickest over the middle of the eye, 

 manifestly for protection. Under this is the second or middle 

 membrane, which is very delicate and soft, and at the centre 

 perfectly transparent. Under this is the third layer, a mucous 

 lining. This is functionally the palpebral lubricant. Thus the 

 outer covering of the eye is really a part of the scarf, extending 

 from the snout to the end of the tail. 



In an old Boa or Python are over two hundred pairs of ribs. 

 These begin immediately back of the atlas or first vertebra and 

 extend to the beginning of the tail — that is, where ihe dorsal 

 vertebras end and the caudal series begins. The abdomen of a 

 snake is covered with transverse parallel scales, or scutes. These, 

 when set on edge and acted upon by the ribs, become a vast 

 mechanism of motor propulsion. For this purpose the ribs are 

 all functional. A pair of serpent's ribs form almost a circle, and 

 can perform a fore and aft movement, and can be operative 

 through the circumference of the body except immediately in the 

 dorsal region. We shall see that the ribs have all to do with the 

 act of exuviation. It is hardly a figure of speech to say, as will 

 be shown, that with his ribs the serpent creeps out of his old 

 clothes. 



In the pines of New Jersey is a fine colubrine serpent, the Pity- 

 ophis melanoleticiis. I have kept these for years in my study, and 

 will give substantially a paragraph from my article already re- 

 ferred to as in the American Naturalist. It describes the exuvi- 

 ation of the Pine Snake as I witnessed it on the floor of my library: 

 When I first saw it I noticed that the skin at the snout was torn, 

 and that denudation had proceeded from the head to some two 

 inches of the neck. The divesting at first glance had a sort of 



