XII DIGESTIVE ORGANS EGGS LUNGS 499 



deferentiii opeu iuto the dorso-lateral })ortious <-»f llie walls of the 

 urodaeum, but the spernia is conducted by folds of the lining of 

 this chamber towards tlie bases of the copulatory organs, which, 

 althoufrh arisint' from the lateral and posterior corners of the 

 cloaca, where uro- ami procto-daeum meet, are stowed away outside 

 the cloaca. These organs are always paired. The proctodaeum 

 or outermost cloacal chamber is shallow. Its inner opening is 

 round and is furnished with a sphincter, but it is surrounded and 

 covered by lips of the outer skin, which form a transverse slit. 

 This is due to the peculiar arrangement of the copulatory 



organs. 



Each organ consists of a tube of erectile tissue, and can Ijc 

 everted like the finger of a glove. To the apex of the tube is 

 attached a long retractor muscle, which arises from the ventro- 

 lateral surfaces of the caudal vertebrae and extends a considerable 

 distance back. AVhen at rest and withdrawn the organs form slight 

 conical, longitudinal swellings on either side of the root of the 

 tail, an external feature l)y which male specimens can generally 

 be distinguished. Only one organ is inserted at one time. 



The majority of Autosauri lay eggs, surrounded by a, white 

 or yellowish shell, which is either hard, for instance in Geckos, 

 in Lacerta viridis and Z. agilis, or parchment - like, e.g. in 

 Chameleons and in L. vivipara. Eggs with a thin and soft 

 shell sometimes exhibit the paradoxical feature of increasing in size 

 after they have been laid. This is explained by the growth of 

 the embryo, which stretches the shell and does not merely live 

 upon the white and yellow contents of the egg itself, but also 

 takes in air and moisture. j\Iany Lizards do not lay their eggs 

 until they contain ripe embryos, which burst the shell shortly 

 after deposition. Some, for instance Lacerta mvii^ara, Angvis 

 frcigilis, and Chamaeleo pumilus, are practically viviparous. 1 he 

 embryos, especially those which are enclosed in hard - shelled 

 eggs, are provided with a shaq), calcareous " egg-tooth " on the 

 top of the snout. 



The lungs are thin-walled sacs, sometimes provided with 

 lateral ex-saeculations, and these reach their greatest development 

 in the Chameleons. The breathing is effected by the motion of 

 the ribs. Inflatable sacs on the throat, or on the sides of the 

 neck, for ornamental or sexual i>ui])oses, occur in various families. 

 The lungs of much-elongated, snake-shaped Lizards are generally 



