36 C. H. TURNER. 



to it, and remounts to the surface in a dry milieu when it is going 

 to form its spores which serve its multiplication. Its hydro- 

 tropism is positive. This is the case with the beetles of the genera 

 Ilaliplus and Hydroporus. Wheeler (1899) had taken from a 

 pool a tuft of aquatic plants where these insects swarm. He 

 says: 'As soon as the beetles could come out and disengage 

 themselves from the plant they turned, with a common accord, 

 toward the sea and to it directed their steps. As this was a 

 distance of about twenty feet, the little creatures could not see 

 the water, and I was led to believe that they had some means of 

 perceiving a source of moisture and acted accordingly. 



"Aquatic bugs act the same way when they are taken from 

 the place in which they live, and we know that the land crabs go 

 a long distance to water when they are ready to place their 

 progeny. The proper degree of humidity differs, moreover, with 

 different species. Wheeler reports that Bembidium, Elaphrus, 

 Omophron, and other small Coleoptera which bury themselves 

 in the sandy beaches, leave their burrows and come out into the 

 open air when one throws a little water on their strand. This is 

 negative hydrotropism. It is well known to collecting ento- 

 mologists, who use it in making captures." 



Weiss 4 reports two cases of what he calls positive hydrotropism. 

 When specimens of the wingless Gerris marginatus were removed 

 one to nine yards from the pond they immediately returned to 

 it. When removed ten yards from the water they had some trou- 

 ble in getting started in the right direction; but finally reached 

 the pond. Thirty yards from the water they seemed to be lost. 

 The case of Dinentes assimilis, a winged beetle, is even more 

 interesting. When removed nine or ten feet from the pond it 

 tried to walk to the pond, then arose and flew directly to it. 

 When removed to a distance of seventy-five feet, it walked 

 about in all directions, then arose, on its wings, to a height of 

 twenty feet and flew directly to the water. When removed 

 half a mile from the pond, it soared in a widening sub-spiral to a 

 height of seventy-five feet and then flew off in the direction of the 

 water. He does not know whether it reached the water or not. 



It is not claimed that the above resum6 contains all that has 

 been written on this topic. It is quite likely that some articles 

 have been overlooked. However, the fact that a diligent search 



