SIII.] THE FKOG. 15 J 



What performs tlie function of the lower eyelid in Man, is i 

 fold of the integument of which very little is pigmented anc 

 which is, for the most part, semi-transparent, so as to re- 

 semble the nictitating membrane of a bird rather than ar 

 ordinary lower lid. If the surface of the cornea be touched 

 the eyeball is drawn inwards under the upper lid, whicl 

 descends a little, at the same time as the lower lie 

 ascends over the ball, to meet the upper lid and close the eye. 



As is well known, Frogs emit a peculiar croaking sound 

 their vocal powers being more especially manifested in th( 

 breeding season, when they collect together at the surface o 

 ponds, pools and sluggish streams, in great numbers. At this 

 season, which commences in the early spring for the Grass 

 Frog, but much later on in the year for the Edible Frog, the 

 male seeks the female and, clasping her body tightly wit! 

 his fore-limbs, remains in this position for days or ever 

 weeks, until her ova are discharged, when he fecundates there 

 by a simultaneous out -pouring of the seminal fluid. Shortl} 

 after the eggs pass into the water, the thin layer of viscic 

 albumen, secreted by the oviduct, with which each egg is 

 surroundedi swells up by imbibition and, with that which 

 surrounds the others, it gives rise to a gelatinous mass in 

 which the eggs remain imbedded during the early stages ol 

 their development. 



The development of the eggs is closely dependent upon 

 temperature, being greatly accelerated by warmth and re- 

 tarded by cold. The process of yelk-division, which com- 

 mences within a few hours of impregnation, is readily 

 observed when the eggs are examined as opaque objects 

 under a low power of the microscope. 



While still within the egg the embryo assumes the form 

 of a minute fish, devoid of limbs and with only rudiments of 

 gills, but provided with two adhesive discs on the ventral 

 side of the head behind the mouth. 



