CAS ANATOMY OF VERTEBRATES. 



almost as completely as in the bird, though in most retaining 

 some flexibility. In the Painted Terrapin (Emys picta) the ova- 

 rian ejrss do not show much difference in size until the seventh 

 year, and oviposition does not begin before the eleventh year. 

 Agassiz is of opinion that all American Emydians begin to lay 

 eggs from the eleventh to the fourteenth year, when individual 

 growth is checked and proceeds more slowly. Each species 

 makes a single nest, and lays the eggs of that season at one time. 1 

 Emys picta digs with the hind legs a perpendicular hole near the 

 stream she frequents, and may repeat the operation several times 

 before selecting one as fit for oviposition : in this she deposits 

 from five to seven eggs. The Snapper ( Chelydra serpentina) exca- 

 vates at first directly downward and then laterally, making the 

 widest part of the hole where the eggs are deposited on one side 

 of the external opening. When the eggs are laid, the female 

 tramples down and smooths over the earth, so that, when dry, 

 the place is hardly noticeable. She lays from twenty to forty, 

 about the size of a walnut. Cinosternon lays only from three to 

 five eggs. Nanemys guttata is usually limited to two or three 

 eggs. Land Tortoises rarely lay more than four or five eggs at a 

 season, and make the nidamental burrow in dry ground. The 

 Gopher (Testudo Carolina, L.) has a dwelling burrow, but forms a 

 separate cavity near its mouth for oviposition : in this the female 

 lays five eggs, then fills the nest up with earth, and flattens it 

 down smoothly by her own weight. 



The TrionycidcB lay from twelve to twenty eggs, or more, of 

 the shape and size of a musket-ball, in a hole in the sand near the 

 water's edge. The shell is thick and brittle. 



The Sea Turtles ( Chclone, Sphargis) are the most prolific of the 

 order. They oviposit in May or the beginning of June, in dry 

 sand, on the shore above high-water mark. The female selects a 

 still moonlight night, when her senses of hearing and seeing may 

 best avail her to detect an enemy. If satisfied, she proceeds to 

 scoop out the sand with her hind fins, using them alternately, and 

 when the sand has accumulated behind her, she scatters it abroad 

 by violent jerks of the paddles ; a hole being made between one 

 and two feet in depth, the eggs are dropped in one by one, and 

 disposed in regular layers to the number of from 150 to 200. 

 The period of the entire operation may be half an hour. When 

 concluded, the Turtle scrapes the loose sand back over the eggs, 

 and makes the surface level and smooth. She then retreats to the 

 water, and leaves the hatching; of the ec;2;s to the heat of the sand. 2 



1 CCC. Part iii. p. 500. " Audubon, quoted in ccexvu. p. 4, and ccc. Part ii. p. 32S. 



