290 AMERICAN TESTUDINATA. Part IL 



run through the bone and open outward by a fine slit in that bridge. The 

 Crocodiles have one large musk gland on each side near the inner and lower 

 edge of the two branches of the loAver jaw, not far from their posterior angle. 

 The position of these glands is nearly the same as in Testudo. Many Saurians 

 have similar glands on the lower surface of the thigh. In Chelydra there are 

 no such glands, though they emit a musk-like stench, quite as strong as that of 

 the Cinosternoidae. It is however possible, that in this family the odor arises 

 from a large number of small glands opening between the warts of the skin ; 

 but I neglected to examine this point in the proper season. Though the pro- 

 duct of these glands may be of some use in keeping the skin fat and elastic, 

 still its more important function may be to enable the sexes to find each other 

 at the time of copulation, as we observe it so plainly in Snakes. 



SECTION XIV. 



THE DEVELOPMENT OF TURTLES FROM A ZOOLOGICAL POINT OF VIEW. 



The growth of Turtles is exceedingly slow. In this respect they differ greatly 

 from the Batrachians, which complete their growth, either entirely or nearly so, 

 during the first year of their life. The true Reptiles, on the contrary, acquire 

 slowly the age of maturity; and among them the Tvu'tles are the slowest in their 

 growth, and acquire latest, as far as we know, the period of puberty. I have 

 collected data which prove satisfactorily that our common Emys (Chrysemys) picta 

 does not lay eggs before it is ten or eleven years old; and even then it is by 

 no means full grown. 



Like most other Reptiles, Turtles lay their eggs either in moist ground, or in 

 dryer places near the water, (fresh-water Turtles,) or in dry ground, (land Turtles,) 

 or in hot sand, (Chelonioidoo.)^ The embryo breaks through the shell of the egg 

 by means of the horn it has upon its snout, (see above, p. 288,) after an incuba- 

 tion varying, in different genera or families, from six weeks to three or four 

 months and even more.^ The outline of the carapace of all Amydse, at the time 

 of its formation, is remarkably similar, namely, ovate, or orbicular and flat; at least, 

 this is the case with all the young which I have had an opportunity to see. 

 There may be an exception with reference to these features in Testudo only, 



^ Respecting the laying of the eggs, more will ^ For more details respecting the act of incuba- 



be found in Part III. tion, see Part III. 



