28 THE DEVELOPMENT 



be remembered that at this period the mouths of these animals 

 were not furnished with teeth. The diagrams given in this number, 

 Plate IV., show vertical and somewhat oblique sections through 

 the mouths of two of them of March 30th (that is the day on 

 which they commenced to feed), and as in none of the sections 

 cut was there any vestige of even the rudiments of teeth, it must 

 be conceded that these structures would not have been elaborated 

 sufficiently for use within two days. 



The mode in which they obtained their food was by applying 

 their mouths as closely as possible to the object, and sucking away 

 at it so as to obtain any liquid or semi-liquid nourishment capable 

 of being extracted. This day, April 2nd, a few animals died, and 

 within the course of the next twenty-four hours many of the living 

 were engaged in devouring them. At the very first we see, therefore, 

 that the tadpole of the frog can live on decomposing animal 

 matter ; and that this is more agreeable to them than green living 

 vegetable matter was shown by the relative sizes of the animals 

 thus kept, and of those living in the tank where there was but little 

 animal matter and excess of vegetable in comparison. These 

 latter were not nearly so large or vigorous as the former ; indeed 

 they were not so vigorous as those which had been kept in the 

 dark, and fed on animal food. 



The only animal food that ever disagreed with tliese creatures 

 was the spawn or Glochidia of the mussel. Some few years since, 

 I took a quantity of these Glochidia from the gills of a large fresh- 

 water mussel, and placing it in a tank where a number of tadpoles 

 had been thriving, watched the result. No sooner was the spawn 

 at the bottom, than the tadi)oles either saw or smelt it out, rushed 

 at it madly, some of them literally wallowing in it, rolling over and 

 over, apparently rejoicing in such a delicate tit-bit. Here, then, one 

 seemed to have procured something in which the litde creatures 

 took special delight, but whether they ate too greedily of the 

 tempting morsel and died of repletion, or whether, as is probable, 

 the triangular shell of the Glochidia proving too much for their 

 digestion stuck in the alimentary canal, and thus produced 

 inflammation and death, certain it is that of the whole colony not 

 one was alive next day, and I, taking care to benefit by this experi- 

 ence, have never since attempted to feed tadpoles on mussel 

 Glochidia. 



