HABITS. EXTINCT FOHMS. 411 



some of the hepatic veins as well as the three systemic veins. 

 The auricular septum is complete, but the ventricular septum 

 is incomplete. The pulmonary artery and the left aortic arch 

 arise from the right side of the septum, the right aortic arch from 

 the left. The right arch gives off two innominates (Fig. 232) ; 

 the left arch gives off the coeliac. The pulmonary artery is 

 connected with the systemic on each side by open ductus Botalli. 

 The apex of the ventricle is as in the Crocodilia connected with 

 the pericardial wall by a ligament. There are two anterior 

 abdominal veins (p. 326). 



The copulation may last a day, and during its process the 

 male is carried on the back of the female. The eggs are laid in 

 small number except in the marine forms in 

 which they are more numerous. They contain 

 within the shell, which is either parchment-like 

 or hard and calcareous, a layer of albumen sur- 

 rounding the yolk, and are buried in the earth, 

 in the aquatic forms near the shore. Accord- 

 ing to Agassiz (I.e.] the North American 

 marsh tortoises lay eggs only once a year, 

 while they copulate twice (in the spring and 

 autumn). The first copulation, according to 

 this investigator, takes place in Emys picta, in 

 the seventh year, the first deposition of eggs 

 in the eleventh year of the animal's life. 

 These facts agree with the slow growth of the 

 body of tortoises and the great age which they 

 attain. 



The Chelonians belong mainly to warmer climates, and live 

 principally on vegetables. Many of them, however, also eat 

 mollusca, Crustacea, fish, etc. Terrestrial, fresh-water, and 

 marine forms are known, and there are about 260 living species. 



The earliest remains of Chelonia are from the Upper Trias 

 (Keuper) and present no approximation to any other form of 

 Reptile. According to the present state of our knowledge they 

 reached their greatest development towards the end of the 

 Mesozoic and in the earlier part of the Tertiary period. 



As an interesting indication of the incompleteness of the 

 geological record, and of the inadvisability of concluding that 

 because fossil remains are not found at any particular period, 



