REPTILES 



371 



Walls, 1942) (Plate VII ).^ In the land tortoises the colours are less 

 bright, brown predominating. The common box tortoise, Testudo 

 Carolina, is peculiar in that it shows a remarkable instance of sexual 

 dimorphism, the iris of the male being red, of the female brown. 



'».*»^^ •;t*i^ » *^* •««*»*• •• 



Fig. 447. — The Posterior Segment of the Eye of the Tortoise. 



1, tlie retina ; 2, choroid ; 3, scleral cartilage ; 4. fibrous sclera (X 112) 

 (Katharine Tansley). 



Fig. 448. — The Ciliary Region of the Eye of the Tortoise. 



Note the immensely thick corneal epithelium, the scleral ossicles, O, 

 arranged in layers, the trabecular tissue forming a pectinate ligament across 

 the angle of the anterior chamber, and the highly developed sphincter of 

 the pupil. The vessel lying internal to the angle of the anterior chamber is the 

 ciliary venous sinus, homologue of the canal of Schlemin ( X 60) (Norman 

 Ashton). 



1 This matching of the colour of the iris to form an "eye mask" in a uniform 

 pattern with the colours of the head is also well seen in such fish as (he lidless 

 lion-fish, Pterois ; in Amphibians, such as the frog, Rnna sjiJienocephala, the newt, 

 Triturus torosiis : in Reptiles, such as the tree-snake, Oxyheli.^ (See Cott, 1940 • O'Day 

 1942). ' ' ^' 



