42 Journal New York Entomological Society. [Vol. xxij 



class of rare or local species, and there is a great difference between 

 species in respect of flexibility, as I have shown in treating the dis- 

 tribution of Cicindela. 



The influence of light and shade appears to be marked in the case 

 of Agabctcs actiductus, found only in woodland pools, but in general 

 the amount of light which penetrates the water must be so reduced 

 that its further diminution by the shade of trees cannot be of great 

 importance. 



The Gyrinidse circling about the surface of the water in broad 

 daylight shun the light less than most aquatic beetles, which will 

 usually be found during the day among the mosses and leaves or hid- 

 ing in the banks. 



Temporary pools afford little in beetle life, and were it not for the 

 beetle's nocturnal errors, would perhaps contain nothing. As a rule 

 the presence of vegetable or animal matter, food of some sort, is a 

 positive requirement for successful water beetle fishing. Given food 

 even the lowest temperatures seem of little consequence ; I have seen 

 water beetles swimming beneath transparant ice thick enough to bear 

 my weight, and Mr. Engelhardt can bear witness to the numbers that 

 we found in the bitter cold pools of Labrador. No beetles were there 

 more numerous than the water beetles. 



In conclusion it seems to me that while the environment may be 

 somewhat varied for many species that are capable of adapting them- 

 selves to varied conditions, the species that might perhaps be called the 

 common species, the environment for others, the so-called rare species, 

 must be exactly right or they cannot maintain their existence. And 

 even for such, an element of accident also comes into play, for such 

 beetles are often missing where the environment is found. Every lily 

 pad does not support a Donacia. In traveling to Staten Island once 

 via New Jersey trolley road, I was told that the trolley car connected 

 with a boat for Staten Island. Arriving at the terminus, no boat was 

 in sight, nor did one appear for a long time, so the environment being 

 right and the boat missing I questioned the dock man, and learned 

 that there was " a car agin every boat but not a boat agin every car." 

 So the student of environment must not be discouraged by apparent 

 failure to connect the beetle with the environment, but remember that 

 there is not always a " boat agin every car." 



