The Development of the Frog 31 



From the ectoblast are derived the epidermis 

 and the various structures derived from the 

 epidermis, such as hairs, nails, etc.; the central 

 and peripheral nervous systems ; parts of the 

 eye, ear, and nose ; the lining of the mouth 

 and anus ; and the pineal gland and pituitary 

 body. 



From the entoblast are derived the lining 

 epithelium of the digestive tract, with all its 

 diverticula, such as lungs, liver, etc.; and the 

 notochord ; though there is some difference of 

 opinion as to the origin of the latter structure. 



From the mesoblast are derived all of the 

 other organs of the body, such as bones, 

 muscles, blood, blood-vessels, and uro-genital 

 organs. 



The development of the more important 

 organs of the body will now be described, and 

 it will be best to complete the discussion of 

 each organ in turn, rather than to attempt to 

 describe their synchronous development. 



DEVELOPMENT OF THE NERVOUS SYSTEM 



Since the nervous system is one of the first 

 to make its appearance in the frog, as well as 

 in other animals, it is a convenient one with 

 which to begin the discussion. 



