IGUANA TUBERCULATA. 365 



warm ; so that more insects in general live, snch as flies, &c, "which are 

 the food of the lizard. Lizards sleep in cold weather, and are therefore 

 sleepers or not sleepers according to the climate. In this climate they 

 would sleep half of the year : in Jamaica perhaps not at all. They 

 become very fat before the cold comes on ; and by the end of the winter 

 they become very lean. This shows they have been absorbing their fat 

 for nourishment. 



Of the Male Parts 1 . — Lizards have two penises, which are in structure 

 similar to the two horns of a snail ; for when erect, they are only an 

 everted canal, or tube, with a muscle arising from the tail and running 

 through the centre to pull them in, or invert them. There are two 

 ridges which make a groove ; this is on the outside when the penises 

 are external, but upon the inside when they are reinstated. 



Of the Eggs. — The eggs of the lizard seem to advance within the 

 abdomen nearly equally fast, not in a regular succession, as in the hen. 

 They seem to remain for some time in the abdomen after they appear 

 to be at their full growth. 



I should suppose that the egg is but a very short time in the oviduct, 

 as I never found one there. I should likewise suppose that the skin 

 [chorion or outer coat] is formed in the oviduct. 



Of the Organ of Hearing. — All of this order, as far as I know, have 

 no external ear. The membrana tympani is almost on a level with the 

 skin of the head ; it is convex externally, or rather appears to be pressed 

 out in the middle. 



[Genus Iguana.] 



The Guana 2 [Iguana tuber culata, Linn.]. 



In this lizard the thorax and abdomen are one cavity, there being no 

 diaphragm. The heart is at the upper part of the thorax, the basis of 

 which is higher than the first ribs ; the upper part of the sternum and 

 bones of the shoulder making part of the cavity of the thorax in this 

 animal. The heart is enclosed in a very strong pericardium which is 

 in contact with the convex surface of the liver 3 . 



The stomach is similar to a bent gut ; it is not a large bag, of a 

 particular shape, as in the human, but rather as if the great end of that 

 viscus in the human was cut ' off : it lies more from behind forwards 

 than in most animals, as it were obliquely, the oesophagus being close 



1 [Hunt. Preps. Phys. Series, Nos. 2426—2437.] 



2 [The skeleton of this animal is No. 666, Hunt. Osteol. Series.] 



3 [The structure of the lungs is shown in the Hunt. Preps. Phys. Series, Nos. 

 1107, 1108, 1109.] 



