I.] THE FROG. 35 



which covers the base of the inner digit in the males, large 

 papillae with interposed glands are developed. 



A singular spheroidal sac-like body known as the hi'owspot 

 or inter-ocular gland, occurs in the integument of the fronto- 

 parietal region of the head. In the young animal it is in 

 connection with the pineal gland, and represents the rudi- 

 ment of the median or pineal eye — a structure which is 

 more fully developed in some Lizards. 



Cells containing pigment abound in the integument and 

 undergo remarkable changes of form, the pigment being 

 sometimes drawn together into a spheroidal mass — at other 

 times distributed in a radiating fashion. 



LABORATORY WORK. 



Frogs may best be killed with chloroform. Place the 

 animal under an inverted tumbler together with a square 

 inch of cotton-wool saturated with chloroform; cover with 

 a cloth and leave for lo — 15 m. 



A. General external characters. 



1. Its division into head^ trii?ik, two pairs of /i?nl?s or 

 appendages. 



2. Its antei'ior or head end; pointed and bearing the 

 mouth, eyes, and other organs of the higher senses. 

 Its posterior or tail end. Its dorsal or back region ; 

 clad in a darkly coloured integument. Its ventral 

 or belly region ; clad in a whitish integument. Its 

 lateral or side area ; bearing the two pairs of limbs. 

 (Work over the specific characters given on pp. 6, 7.) 



a. The head. 



Somewhat triangular, with tlie blunted apex 

 turned forwards and passing, without any neck- 

 constriction, into the trunk. 



