44 LABORATORY DIRECTIONS IN 



6. After Several Months or a Year (According to the Species Used). 



5;'. Tadpole with hind legs. Note the following external features 

 observed in the eighth day tadpole: tail, fin, myotomes, mouth, eyes, and 

 nasal pits or nostrils. In addition find: 



The hind legs. The forelegs are present but concealed. 



The spiracle, an opening on the left side. Its front edge is the edge of 

 the operculum (see stage 4) which has fused with the body everywhere 

 except at this point. Water passes out of the gill chamber through the 

 spiracle. 



The horny jaws with which the tadpole scrapes off little particles of 

 food from objects in the water. 



The myotomes or muscle segments along the sides of the body and 

 tail. Strip off the skin from a part of the tail and with a sharp needle 

 tease apart the muscle fibers of a myotome. Note whether the muscle 

 fibers extend beyond the connective tissue septa. 



Internal Features. Slit open the body wall on the ventral side and 

 turn the flaps back. Observe: 



The much coiled intestine, and the mesenteries supporting its coils. 



The liver, a brownish body to the right of the intestine (the observer's 

 left), and the gall bladder, on the posterior side of the liver. 



The pancreas, along the anterior part of the intestine. 



The heart with its whitish ventricle anterior to the intestine. Push 

 the intestine to one side and beneath it find : 



The fat bodies, branching yellow organs. 



The two kidneys lying against the dorsal wall in the posterior part of 

 the body cavity. 



The small reproductive organs lying near the anterior ends of the kid- 

 neys. It is difficult to distinguish the sexes at this stage. 



The lungs, two flattened black or grayish structures attached at the 

 anterior end of the body cavity and free at their posterior ends. They are 

 rudimentary and still functionless at this stage. 



Open the gill chamber by slitting through the operculum and observe: 



The brownish fluffy gills. Probe between them into the mouth. The 

 openings from the gill chamber into the mouth and pharynx are the gill 

 slits. 



The fore legs inside of the opercular cavity behind the gills. 



C. SUMMARY 



Describe carefully, but without too much detail, the essential features 

 of (a) maturation and (6) development. Trent both phenomena as con- 

 tinuous processes, not as a series of stages. That is, fill in the gaps be- 

 tween the stages studied in the laboratory. 



