they will not be poisoned by disintegrating egg-jelly, and placed in a balanced 

 aquarium. After the first few days, when they begin to swim actively about 

 in search for food, a little powdered dog biscuit or fish food may be added. 

 Many tadpoles appreciate tiny worms or bits of raw meat. Care should be 

 taken not to overfeed. In order to keep the v^ater fresh, uneaten fragments 

 should be quickly removed. As the hind limbs become well developed and the 

 nose of each tadpole takes on a more pointed shape, the water level should be 

 lowered and the aquarium tilted, making it possible for the tadpoles to lie with 

 their bodies partly exposed. This is necessary because the arms have grown 

 into the gill chambers, intcrfermg materially with the gills, so that the action 

 of the developing lungs must be supplemented by respiration through the skin. 

 As soon as the fore limbs appear externally, the creatures may be removed to 

 a tcrrarium. Small insects, such as fruit flies of the genus DrosophiJa, make 

 excellent food at this time. 



In general, the remarks on study methods made at the end of the sala- 

 mander chapter hold also for frogs. There is much need for study of life 

 histories under natural conditions. Much of the descriptive work has of neces- 

 sity been based on collections made by some biologist during a brief trip into 

 a new area. Such observations may lead to errors. For example, if one finds 

 two size groups of one species he may infer that they represent the year-old 

 and the two-year-old groups, when they might equally well be from two 

 spawnings during one year. Some forms, such as the spadefoot toad, have 

 been reported to spawn at three different times in one year, even in northern 

 states. A collector visiting the ponds and finding well grown tadpoles shortly 

 after the third spawning was reported, and unaware of the earlier spawnings, 

 might easily be deceived into thinking that development was remarkably rapid. 

 Continuous studies, such as those made by the Wrights on the frogs of the 

 Ithaca region, are needed for all forms. Methods of marking individuals, by 

 tattooing or some method not likely to handicap the animal, would make it 

 possible to check on the rate of growth, seasonal migration, age at which sexual 

 maturity is reached, and length of life under normal conditions. 



Hibernation offers another challenge. Where and how far do the animals 

 go in search of suitable hibernation quarters? How do they avoid freezing 

 and how much cold can a dormant frog endure? How great is the mortality 

 during hibernation? 



Choice of breeding sites also is in need of study. How far do the animals 

 go in search of a suitable site? Do they return to the place in which they 

 developed? Do they return to the same place each year? Why is one pond 

 selected in preference to another? Why do the American and Fowler's toads 

 of the same area usually select different spawning sites? Is egg-laying cor- 

 related with certain air and water temperatures? 



These are but a few of the questions upon which we need more data and 



335 



