June, 1919] Fauna of Rock Bottom Ponds 467 



The cosmopolitan species were a chironomus larva, a water 

 strider {Gerris), a may-fly (Heptagenia), a protozoan {Ceratium) 

 and the snail Physa. Most of these are species which are to 

 be found in almost any body of fresh water. In the distribution 

 of the forms inhabiting but one pond we find them rather 

 evenly scattered among all the ponds except the one fifteen 

 years old. And so, too, with those present in two, three and 

 four ponds respectively, there is an approximately even distri- 

 bution of them through the series. 



Practically all of these species are commonly found over 

 a wide area. Their manner of distribution in these ponds, 

 therefore, clearly shows that there may be great regional 

 uniformity in the distribution of a species and, at the same time 

 a local absence of uniformity even in habitats which, super- 

 ficially at least, are apparently similar. The data given in 

 connection with the respective ponds is sufficient to show 

 that this condition can be traced in large part to the environ- 

 ment presented by each pond. To determine all of the factors 

 in each case with any degree of completeness would take a 

 much more detailed study extending over a greater period of 

 time than I have been able to give the subject. 



Regarding succession, it is hard to draw general conclusions 

 because, over and above the natural sequence of environmental 

 changes w^hich is to be expected, each pond has a peculiar set of 

 conditions which complicates the problem. However, a certain 

 degree of faunal development is evident. 



In the year old pond the following groups had become 

 estabhshed: Coleoptera (larvae and adults), Diptera (larvae), 

 Ephemeridce (nymphs), Hemiptera (nymphs and adults), Tri- 

 coptera (larvae), Arachnida, Entomostraca, Mollusca (snails). 

 Rot if era, Hirudinea, Protozoa, and, if we exclude Char a as 

 antidating the pond, filamentous alg«. The prominent faunal 

 features in this pond are the great abundance of insects both in 

 species and in individuals of certain species; also the fact that 

 there were no vertebrates and, with two exceptions {Arachnida 

 and Mollusca) fewer species of any other group than in any of 

 the other ponds. 



Insects composed twenty-seven out of forty-three species. 

 There are both environmental and morphological reasons for 

 this. Wings and flying as a means of locomotion enable insects to 

 reach an isolated body of water before other forms which might 



