DEVELOPMENT OF THE COMMON FROG. 97 



from time to time, but not closely examined. The ova on 

 the surface of the mass, however, were seen to be hatched ; 

 and the tadpoles had escaped before those deeper in the 

 mass began to develop, so that there was a difference of 

 about a fortnight in the hatching of those at the surface 

 and those in the centre. 



At this time, namely the 25th of April, all the tadpoles 

 had escaped, and nothing was seen but the mass of gela- 

 tinous matter which had surrounded the ova and still held 

 together. I had frequently looked very carefully round the 

 borders of the pond for tadpoles, but could find none ; 

 now, however, on plunging a large basin into the midst 

 of the gelatinous mass, hundreds of tadpoles were at once 

 washed into it with the water, and it was evident that the 

 pond would furnish an abundant supply for further obser- 

 vations. 



The water of the pond was at this time so clear that in 

 the sunshine every part of the bottom could be clearly 

 seen. It contained a few water-boatmen and about half 

 a dozen sorts of beetles. The sides were well grown over 

 with confervse, which formed a rich green pile covered with 

 large air-bubbles. 



23rd. I examined several of the pond tadpoles, and found 

 no advance in them from the last drawing. The tadpoles 

 in the pond appeared to be in development slightly behind 

 those which had grown in the house. 



24. A tadpole was killed and a drawing made of its 

 lower surface. The gills were still rather large, but were 

 dark-coloured and opaque. There was an appearance as 

 if the opercular fold were preparing to join to the skin 

 of the abdomen, the latter forming a slight raised ridge 

 to meet it. The suckers were smaller than before, but 

 were evidently efficient, as they were in constant use by 

 the living tadpoles, which always remained stationary un- 



