THE PROG; Rana temporaria and R. esculenta. 



Examine a living frog in an aquarium, noting, — the walking, leaping, and swim- 

 ming movements ; the colour of the skin under different circumstances ; the attitude 

 when at rest ; the depressed rounded body ; the absence of a neck and tail, the short fore 

 limbs and the inverted manus ; the sacral " hump " at junction of vertebral column 

 with urostyle ; the long femur and crus, and the greatly elongated webbed pes. Study 

 movements of external nostrils and floor of mouth in respiration ; the elevation and 

 depression of lower eyelid, and, if possible, the method of feeding ; and in the male 

 edible frog the expansion of the vocal sacs during croaking. 



A. External Characters. 



1. Make an outline sketch of the frog from the side, and indicate — 



(a) The mottled colour of the skin. 



(6) The eye, with the semi-transparent lower eyelid half raised. 



(c) The interocular gland and the dark patch behind the eye containing 

 the tympanic membrane. 



(d) The extent of the gape, the position of the external nostrils, and the 

 opening of the cloaca. 



2. Sketch— 



(a) The manus (4 times nat. size), showing callosities on palmar aspect, 

 and if a male the swollen cushion at base of index. 



(&) The pes (2 nat. size), showing the long tarsal region and the 

 webbed digits. 



3. Number the digits in both limbs from within outwards, noting the short 



hallux (I) with a spur at its base, and the long IV. digit of the pes. 



4. Examine (low power) and sketch — 



(a) A portion of the web showing the branched pigment cells and the 



blood-vessels. 

 (6) A portion of the epidermis, showing openings of unicellular and 



spherical cutaneous glands. 



