Class 4. Reptilia. 421 



folds) is inserted into the cloaca of the female ; the sac is withdrawn by 

 a muscle attached to its end. In the Crocodilia and Chelonia, 

 the penis is, on the other hand, an unpaired, solid, linguiform organ 

 which is attached to the ventral wall of the cloaca, and can be 

 protruded from the anus ; it has a seminal groove on its upper surface. 

 The eggs of Reptiles are relatively large. During their passage 

 through the cloaca, they are surrounded by albumen and a calcareous 

 shell, which in Lacertilia and Ophidia, is usually leathery and tough, 

 in Crocodilia and most Ohelonia hard and brittle, like a Bird's egg- 

 shell. The shell is usually oval, occasionally round, the latter in 

 most of the Chelonia. The eggs of not a few Ophidia and some 

 Lacertilia remain so long in the oviductSj that the young ones are 

 born alive. The eggs of such forms are usually provided with shells 

 which are thrown off at birth. Segmentation is partial, food yolk 

 abundant; the embryo is surrounded by embryonic membranes 

 {see p. 353). The animal, when newly hatched, is in most respects 

 like the adult. 



In the fully-developed embryos of Opliidia and Lacertilia, there is a median 

 tooth on the upper jaw (a true tooth) which is used to cut thi-ough the egg-shell. 

 The embryos of Crocodilia and Chelonia have, at the tip of the snout, a wait- 

 like, veiT^ corpified projection, with which to break the shell. 



The Reptilia are for the most part terrestrial; but a few 

 are amphibious, for they live partly in the water (sea or freshwater), 

 partly on land ; most of them prey on other animals (Insects^ 

 Yertebrata, etc.). They are numerous in the tropics, occur sparingly 

 in temperate regions, and are absent from colder zones. At earlier 

 periods of the earth's history, in Mesozoic times, this division 

 was much better represented, and, in part, by much larger forms 

 than at the present time. 



Synopsis of Existikg Oedees of Reptilia. 



r 



Movable quadrate. Anus 

 a transverse sUt. Paired 

 copulatory organs. 



slit. Penis unpaired. 



Lacertilia. Usually with limbs. Scales ven- 

 trally. Rami of lower jaw fii-mly anchylosed. 

 Ophidia. Without limbs. Splints ventrally. 

 Rami of lower jaw connected by an elastic Hga- 

 ment. 



Quadrate immovable. P' Ohelonia. Edentulous. Continuous bony 



Anus not a transverse \ , ""^^^ ^""^.'^^ .*^« ^^"f^- . 



4. Crocodilia. Teeth m sockets. Heart with 



two ventricles. 



Order 1. LacertUia {Lizards). 



For the characters of the Lacertilia, compare the above summary, 

 and the general description of the Reptilia. Of the numerous forms, 

 a few examples are given below. 



