170 



THE YOUNG NATURALIST. 



escape from the capsules at least 24 hours sooner that those from the bottom 

 layer. Yon will see by the specimens on the table, which were taken out of 

 water an hour after deposition, that frog spawn consists of small gelatinous 

 spheres £ in. diameter, colourless, and containing each in its centre a small 

 opaque speck T ^in. diameter. Owing to the transparency of the enveloping 

 membrane, the development can be watched through all its stages. At first 

 the embryo appears spherical, dark brown on one side and white on the other. 

 In about three days it elongates, and about the sixth day the head and tail 

 may plainly be seen, as can also the gills and holders, which latter are two 

 small organs near the mouth, enabling the animal to attach itself to the egg 

 case, or to a plant as soon as it leaves the egg sac, which it does about the 

 twelfth day. For two days after its escape the tadpole remains at rest. 

 During this time it breathes by means of the external gills, which subsequently 

 diminish, whilst on either side an operculum or gill cover is formed by a fold 

 of the skin, and internal gills are simultaneously developed. 



The external gills cease to be visible on the eighth day, and the respiration 

 is effected in the capillaries of the internal gills, by the water being taken in 

 through the mouth and expelled through the minute orifices which represent 

 the remnants of the opercular openings. 



The food of these young beings is at first vegetable, though they also eat 

 the remains of the old egg cases ; when older, they eat flesh, and sometimes 

 one another. The development of the limbs is most variable, all depending 

 upon favourable situations and food, so much so, that to-day I have some 

 still in the tadpole state which were hatched on the 7th April, 1887, although 

 their congeners out of doors are now, and have been for some time, in the 

 happy possession of their limbs. The normal time for the first appearance 

 of the hind legs is the fiftieth day, the fore legs appearing seven days later. 

 Three days later the tail is totally absorbed, and the animal has passed from 

 the larval to the adult form : of course it increases in size, being at first only 

 fin. long, but it undergoes no further metamorphosis. These statistics as to 

 the periods of development have been obtained by repeatedly examining a 

 number of ponds and carefully noting the progress made day by day. I 

 have been surprised at the difference in the dates of development, between 

 those bred in aquaria and those in a state of nature; and this difference 

 I attribute to the difficulty of getting suitable food for those in captivity. 

 As an instance of the unreliability of dates obtained by observing animals 

 under artificial circumstances, I may say that some of the tadpoles which 

 hatched out in my room on the 7th April, 1887, were not in possession of 

 their hind-legs until the 31st July, 116 days, or more than twice the length 

 of time required under normal conditions. 



