The Common Leopard Frog 



If we now look at the embryo from above or below, the 

 region of head and neck shows sHght projections. (Fig. 209.) 

 Examining these very carefully from the side, we see the appear- 

 ance shown in Fig. 208. That portion in the most anterior 

 and largest projection or swelling (sense plate), will become 

 the facial part of the head, with upper and lower jaws, mouth, 

 and nostrils. The three smaller elevated portions back of this 

 are destined to make the gills. There is a blunt projection on 

 the lower portion of the head end, which, on account of its posi- 

 tion (the front margin of the sense plate), might be mistaken 

 for a mouth. Viewed from the front (Fig. 209), it becomes 

 one side of a horseshoe-shaped structure which will make, not 

 the mouth, but a pair of " suckers," to be used by the tadpole 

 to attach itself to water-weeds. 



On the sixth day (April 14th) the young tadpoles are still 

 longer and are more curved in the egg. The body seems much 

 thinner. The head and tail ends are unmistakable, even to 

 the casual observer. The projections on the sides of the neck 

 are more distinct. 



On the seventh day the tail is longer and distinctly fmned 

 at its edges. The head is more distinct from the body. The 

 projections at the sides of the neck are longer. The tadpoles 

 occasionally move in the egg, putting the head and the tail to- 

 gether and then jerking them apart. They seem little changed 

 on the following day but move more often. 



On the next morning (April 17th), nine days after the eggs 

 were laid, we fmd most of the tadpoles out of the jelly, clinging 

 by two conspicuous " suckers " to the deserted jelly-mass or 

 to water-weeds. (Fig. 210.) These "suckers" are not what 

 their name would seem to imply. They do their work of cling- 

 ing, not by suction, but by means of a sticky substance or cement 

 which they secrete. The jelly is much less stiff. Other tad- 

 poles hatch as we watch: a vigorous wriggle, and the jelly sphere 

 is ruptured and the tadpole becomes free. The tiny bit of life 

 may lie flat on the jelly or at the bottom. But after a short 

 time it is rested from the exertion and wiggles through the water 

 aimlessly until it touches something that will act as a support. 

 The tadpole is now about 7J mm. long, very slender and black. 

 The transparent tail fm is conspicuous. The projections at 

 the sides of the neck are easily seen as branched fmger-like gills 



179 



