ORGANIC EVOLUTION 207 



and actions. Freshly anesthetized specimens for gross 

 dissection. 



Study the internal organs in the order outlined in the 

 preceding pages; (if fuller outlines are desired, they may be 

 found in laboratory manuals of vertebrate zoology or of 

 general zoology, nearly all of which deal mainly with com- 

 parative anatomy) . Trace the alimentary canal and note 

 its differentiation into parts. Identify its appendages 

 and find their channels of communication with the enteron. 



Inflate the lungs and note the relation between air 

 tubes, air cells and blood vessels. Identify the cham- 

 bers of the heart and trace the main channels of circu- 

 lation. Trace the ureter from the kidneys to the mouth of 

 the urinary bladder. Compare spermaries and ovaries in 

 male and female specimens and trace the ducts for the exit 

 of the sex cells. 



Find the paired spinal nerves issuing from the spinal 

 column and lying against the roof of the body wall, and find 

 the paired sympathetic ganglia in the ccelom attached by 

 commissures, one pair to the roots of each pair of spinal 

 nerves ; look also for nerves extending from these ganglia 

 to other sympathetic ganglia in the walls of stomach, heart 

 or lungs. 



The record of this study may consist in drawings and 

 diagrams of the form and relations of the principal organs 

 studied. 



Study 27. The structures of the body wall of an amphibian. 

 Materials needed: The specimens from the preceding 

 study, if preserved in two per cent, formalin after the 

 removal of the internal organs. Wash free from the formalin 

 in running water before using. Also skeletons disarticu- 

 lated, and a few mounted ones for comparison. Also, some 

 forms with cartilaginous crania, such as sharks, or large bull 

 frog tadpoles for the easy examination of the brain. 



