128 



vegetable substances will afford equable warmth with suffi- 

 cient moisture to prevent the egg drying up through its thin' 

 covering. The eggs are frequently watched by the mother ; 

 some snakes (Pythonidse) incubate their eggs, while the 

 hsuneidr jSidOphiophagus,SiS I am informed on good authority, 

 makes a nest of ' wild plantain' shrubs which by their 

 rotting give off heat and moisture. With regard to the 

 incubation observed in the case of the python, I do not think 

 that much stress can be placed on this point, the heat 

 shown to be imparted to the eggs, though of some use 

 in temperate climates would be scarcely needful in the 

 natural climate of the snake. I have frequently observed 

 Tropidonotus quincunciatus, when it has laid eggs in 

 captivity, to lie on them apparently incubating them ; but 

 I should not infer that it would do so when at liberty, and 

 moreover the eggs so incubated were all shrivelled up. The 

 same fate awaited all eggs which I have kept in sand or 

 sawdust, whether dry or moist ; to hatch the eggs artificially 

 they should be placed in dung heap compost. 



When the young snake is mature it makes its escape 

 from the shell by means worthy of attention. A tooth 

 is developed on the premaxillary for the purpose ;* it is flat 

 and horizontal, being used like a leather-knife ; with it the 

 snake makes several cuts in the end of the parchment shell 

 until, two cuts meeting, a valvular opening is formed ; by this 

 the young snake escapes. In many cases the young snake 

 retains for some time the remains of the navel string (the 

 vitelline duct), and the navel after closing is long visible as 

 a slit in three or four ventral shields at about the thirtieth 

 ventral from the vent ; e. g., the young cobra. But Ptyas 

 mucosus emerges from the egg with the navel closed and no 

 trace of vitelline duct. 



* This tooth falls off soon after the birth of the snake. It must be 

 remembered that in the lower types of snakes the Pythonidce bear 

 teeth on the premaxillary. 



