1 64 ELEMENTARY BIOLOGY. [CHAP. 



rj. The branchial pore (spiracle) ; asymmetrical and 

 on the left side (external branchiae are no longer 

 present). Remove the ventral portion of the 

 adjacent integument (coalesced opercula) ; a 

 spacious branchial chamber will be exposed. 

 Note its limits. 



6. The- internal branchice ; paired vascular folds of 

 the sides of the head, four sets on each side, 

 lying within the branchial chamber. Try and 

 make out their relations. They are borne upon 

 outgrowths of the wall of the pharynx (branchial 

 visceral arches), which alternate with perfora- 

 tions of the same {visceral clefts) putting the 

 pharyngeal cavity in communication with the 

 branchial chamber. 



i. The lungs; seen, on opening up the body- 

 cavity, as small diverticula of the alimentary 

 canal not yet distended with air. 



o. The larva on the appearance of hind-limbs. 



Examine from beneath. 



a. The body generally ; note the proportions of its 

 several constituents. 



/?. The mouth; its large size ; papillate lips and 

 horny teeth well marked. 



y. The absence of suckers and branchial pores. 



S. The hind-limbs; small, but fully differentiated; 

 one-third the length of the body and separated 

 in the ventral middle line by the terminal por- 

 tion of the alimentary canal. 



f. The fore limbs ; differentiated, but covered by 

 (visible through) the opercular membrane. 



