^66 OVIPOSITION AND HABITS OF CERTAIN BATRACHIANS, 



cases the surface of the water being lowered subsequently by evapo- 

 ration or otherwise, such patches may soon be left high and dry 

 with little chance of developing. The frothy appearance of the 

 patches is caused by the entanglement of numerous bubbles of air 

 or gas in the glairy envelopes of the ova, and their accumulation on 

 the surface, quite obscuring the ova which to the number of several 

 hundred lie below. The oviposition of the common European frogs 

 is said to take place at the bottom of the water, the ova being sub- 

 sequently floated to the surface by the disengagement of gas in the 

 substance of the glairy envelopes (the hatching in England not taking 

 place for a month). The frothy appearance of the spawn of our frogs 

 is hardly I think to be explained in this way. In shallow pools 

 they may be said to oviposit at the bottom of the water — and in 

 many cases, though it may be only accidental, it seems as if the frogs 

 preferred to oviposit in shallow water an inch or two in depth, 

 e.g., in rain pools, or in a chain of little pools along the course of 

 overflow of a. pond, or in the water-tables of roads, and which often 

 dry up in a few days' time without the tadpoles having a chance 

 of surviving, and this though more permanent supplies of water 

 may be close at hand ; or round the edges of large ponds. But 

 on the other hand, whether from choice or necessity, frogs cer- 

 tainly do spawn sometimes in deeper water, and then the copulating 

 frogs may be seen floating at the surface, or clinging to the 

 branches of partially submerged shrubs, and they evidently spawn 

 so. Moreover such frothy patches enclosing the still segmenting ova, 

 and sticky enough to adhere readily to anything stationary with 

 which they may come in contact, may be found floating freely ; 

 and by visiting a pond in the evening and then again in the early 

 morning, one may satisfy oneself as to some of its having been 

 deposited during the preceding night, even if one cannot get more 

 direct evidence. Hence it seems to me that the buoyancy of the 

 patches is possibly quite as much dependent on the entanglement 

 of air-bubbles due to oviposition at or close to the surface of the 

 water, or perhaps to some peculiarity in the mode of oviposition, 

 as to the liberation of gases by decomposition in so short a period, 

 more especially as in our mild climate the tadpoles are hatched by 



