DEVELOPMENT OF THE COMMON FROG. 119 



left side, and until, in conjunction with the chambers thus 

 formed, the nasal passages are opened into the back of the 

 mouth. This use of the nasal passages for the aquatic 

 respiration is not mentioned by any of the authors I have 

 consulted, and appears an observation of some importance } 

 for the water so entering leaves the mouth entirely free 

 for feeding. 



The development of the peculiar tadpole-mouth and the 

 enlargement of the abdomen, indicating the formation of 

 the coiled intestine, commences only when the gill- 

 chambers are complete; and these structures are made 

 ready for use within the last three days of the period. It 

 is during these three days also that the remarkable gold 

 spangles in the skin are seen in their greatest perfection. 

 Whilst these developments have been taking place the 

 tadpole has grown much larger, and the tail especially has 

 become more expanded and stronger, so as to form a 

 powerful aquatic locomotive organ. This second period, 

 like the first, occupies fifteen days. 



Third Period. — The third period, extending from the 

 thirtieth to the fiftieth day, appears to be devoted 

 entirely to growth, no new developments being observed. 

 The tadpole swims actively, feeds voraciously, and grows 

 very rapidly. The gills are contained in a chamber formed 

 by the opercular membrane ; and water, entering by the 

 nostrils, passes through the branchial clefts and, after 

 bathing the gills, escapes through the opening at the left 

 side. This opening, which is at first formed by the mere 

 absence of union between the free edge of the opercular 

 fold and the skin of the abdomen, and is seen near the 

 left border of the ventral surface, soon becomes tubular, 

 and gradually extends upwards and backwards, embedded 

 in the skin to about the middle of the left side of the body, 

 where it terminates as a short conical projecting tube. 



