DEVELOPMENT OF THE COMMON FROG. 115 



86. A frog with remains of a tail about three quarters 

 of an inch long, was taken from the pond and examined. 

 A drawing, natural size, was made. 



86 (2) . The skin was then taken from the abdomen ; 

 and after removing the dark-coloured layer beneath it, 

 the viscera were exposed. An enlarged drawing was made 

 of the parts seen; they were the liver, gall-bladder, stomach 

 and intestine, and the left lung, which chanced to be floated 

 up out of its natural position. The gall-bladder was re- 

 markably large, and, as usual, globular in shape and of a 

 dark bottle-green colour. 



86 (3). An enlarged drawing wa3 made of the liver, 

 stomach, and intestine, removed from the body. The in- 

 testine was quite empty. 



86 (4). The left lung was cut off and a drawing made 

 of it under the microscope with the two-inch object-glass. 

 It was floated on water and viewed by reflected light. 



Life-history of the Tadpole. 



The foregoing observations, though superficial and in- 

 complete, appear to afford sufficient material for an out- 

 line sketch of the life of the tadpole, which may be filled 

 in by the results of more elaborate researches. The 

 development of the different organs in orderly succession 

 suggests the division of the life-history into periods, each 

 distinguished by the appearance of certain organs or 

 structures ; and five such periods are naturally marked 

 out — the first extending from the deposition of the ovum 

 to the escape of the young tadpole from the egg, the 

 second from this time to the completion of the alimentary 

 canal, the third to the commencement of the development 

 of the limbs, the fourth to the commencement of those 

 changes by which the larval form of alimentary apparatus 



