MICHIGAN ACADEMY OF SCIENCE. 57 



these tadpoles and newt larvae are not strono- swimmers and would be 

 swept away by swift water. Hence this quiet water or pond habitat 

 is the breeding ground and home of the larvae of all four ampliibians 

 of this series, and the habitat of the mature newt as well. 



The sandy soil of the Douglas I>ake region is not favorable to the 

 formation of ponds, as is a clay soil. As a result, ponds are not common. 

 There are, however, many small, deep lakes and small rapidly moving- 

 streams. Both streams and lakes are unfavorable to the formation of 

 the pond habitat; the streams because of their own movement, and the 

 lakes because of the action of winds and waves during the summer, and 

 of ice-jams which plough up the shore during the winter. Pond condi- 

 tions in this region are restricted therefore, almost entirely to the water- 

 lily associations, which are found in the lakes behind sheltered points, 

 in the quieter portions of the small streams, and in the large beach pools 

 wliich have been cut off from some of the larger lakes. Consequently 

 the young of these four amphibian species of series 1 are concentrated 

 in these favorable localities, and are there often very abundant. 



The bogs of the region offer pond conditions to some extent and these 

 primary amphibian species are usually well represented in the vicinity 

 of a C'lamaedaphne bog (see tables). The Thuja bog however, if con- 

 taining open water, rarely supplies the proper transitional habitats. The 

 transition zone in the vicinity of the Thuja bog is usually a narrow 

 one, connecting tlie bog abruptly with dense forest, a condition more 

 favorable to the primary ampliibian species of series 2. 



The optimum habitat for the species of series 1 in the Douglas Lake 

 region, as shown by the collections and field data, was the beach pool. 

 The grasses and sedges which come into such a pool around its margin 

 form an excellent transitional habitat for the young frogs, and if there 

 be a swampy area of any considerable size adjoining the beach pool 

 proper these same grasses and sedges may form the habitat of the adult 

 frogs as well. Beyond the swampy area the type of plant association 

 is of little consequence as the tension zone between the swamp and 

 almost any other plant association found in the region could be used as 

 a habitat by the adults of these three species of frogs. The ratio of 

 abundance of these three amphibians varied however with the type of 

 plant association beyond the swampy area. It was noted that bullfrogs 

 were more abundant in the vicinity of a beach pool if the vegetation 

 beyond the swampy area were hardwood or thicket than if it were open 

 field or sand beach. In this connection it should be pointed out that, 

 although a given species be listed in the tables as abundant in a partic- 

 ular habitat, it frequently was not abundant in small or isolated units 

 of that type of habitat, the sequence of the adjoining plant associations 



