THE FROG. l6l 



able by the presence of the tail, the lashing move- 

 ments of which are very conspicuous (when at 

 rest it is usually bent round to the right side). 

 Liberate the embryo, and in doing so note that 

 the mucous mass is undergoing disintegration. 



a. The body; now differentiated into distinct head, 

 trunk and tail. 



Examine from the side. 



p. The visceral arches; four in number on each 

 side, the two hindermost bearing papillate out- 

 growths (external branchitz). 



y. The eye ; obvious as a rounded eminence above 

 the interspace between the first two visceral 

 arches. 



8. The auditory organ; obvious as a small pit 

 (auditory pit) behind and above y. 



Examine from beneath. 



e. The suckers ; now at their maximum of de- 

 velopment and probably confluent posteriorly. 



. The mouth ; a deep oval pit in the middle line 

 immediately in front of e. 



fj. The olfactory organs ; apparent as two shallow 

 pits (olfactory pits) in front of the mouth. 



9. The anus (proctodczum) ; a minute pore at the 

 base of the tail. 



k. The free swimming larva. Fish-like and bilaterally 

 symmetrical, tail and external branchiae much 

 elongated. Introduce some duck-weed or other 

 small plant into the water, and note the move- 

 ments and habits of the larvae. 



M. H 



