472 Causes and Course of Organic Evolution 



vertebrae, feeble limbs, poorly ossified pectoral and pelvic 

 girdles seem to be in part primitive, in part — specially as regards 

 the limb girdles — degenerate conditions. 



The Cryptobranchidse are caducibranchiate; the fore and 

 hind limbs are well developed; the digits are 4-5; eyelids are 

 absent; upper and lower jaw bear teeth; the skeleton is in 

 part cartilaginous but is condensed and strong, the vertebrae 

 however are still pseudocoelous; there is a sternal cartilage; 

 the skull is well-formed and osseous, but there are no supra- 

 or basi-occipital or intercalary bones; there are three epibranch- 

 ial cartilages and one mature gill cleft as in last; the carpal 

 and tarsal elements are still cartilaginous, but are numerous 

 (8 to 9); the alimentary canal is extensive, divided into dis- 

 tinct areas, and the intestine is long and greatly convoluted. 



The Amblystomidae are caducibranchiate; the fore and hind 

 limbs are well formed; the digits are 4-5; eyelids are absent; 

 teeth are as above ; the skeleton is only slightly cartilaginous 

 but the vertebrae are pseudocoelous; the skull is closely as in 

 the succeeding; there is one epibranchial cartilage; the carpal 

 and tarsal elements are now ossified and numerous (8-9); 

 the alimentary canal is as in the last. Reference may here 

 be made to the gradual formation of the digits in fore and 

 hind limb as synopsizing the phylogenetic history of the group. 

 "In Amhly stoma punctatum the number of digits succeed each 

 other as follows: First stage, 2 before, hind limb none; second, 

 3 before, hind limb none; third, 3 before, hind limb 2; fourth 

 3 before, hind limb 3. Sometimes the anterior digits are com- 

 plete in number before the posterior foot appears, and we have 

 combinations of number from 4-0 to 4-3, and 4-4 to the full 

 number 4-5, which is found in all specimens of 2.5 mm. and 

 upwards" (152: 32). 



The two last groups show decided transition to the next 

 and last one Salamandridae, the genera Desmognathus and 

 Thorius serving in many respects to unite all three. 



The Salamandridae are caducibranchiate; fore and hind 

 limbs are well developed and relative to the size of the body 

 are set well down from it, so as to raise the animal on them; 



