﻿4 FIELD AND FOREST. 



Having frequently observed hail before, I have never noticed the 

 presence of the spines referred to, and think it a somewhat exceptional 

 phenomena. In the hail-storm, which visited this city fune 21st, 1857, 

 the large stones were all flattened ovals, and much thicker in their 

 short diameter than these just mentioned. On that occasion I meas- 

 ured one an hour after it had fallen with the respective diameters of 

 1 8-10 inches, 1 7-10 inches and 8-10 inches. 



E. M. Sc'HAEFFER. 



Invertebrates which prey upon Fishes, 

 Reptiles and Amphibia. 



During the months of August and September last I had the opportu- 

 nity of observing the habits of some water insects in relation to their 

 contact with the smaller species of fishes. The habits of the cray fish, 

 Cambarus ohesus, were also studied in this connection. A very small 

 aquarium contained about a dozen Cyprinids. A few young chubs, 

 Semotilus corporalis, a few of Argyreus nasutus* and a few red-lined 

 minnows, Ckrosomus erythrogaster. Some fronds of the Anacharis 

 Canadensis did duty as oxygen generators. 



Among these I placed a large water beetle, Dytiscus, a Ranatra and 

 a steamboat bug, Belostoma grandis. For a few hours they seemed to 

 live together peaceably enough. 



During the same day a partly grown green frog, Rana halecina, was 

 put into the aquarium. As he swam awkwardly around the side of the 

 glass case the Dytiscus discovered him and made an eager rush in his 

 direction. The frog was alarmed, whether because he knew he was 

 near an enemy, or that any confusion or movement in the water in- 

 creased his agitation, incited by captivity, was not easy to decide. 

 The frog passed out of sight behind the leaves of the plant, but was 

 not wise enough to remain in comparative safety and continued his 

 journey around the glass. The Dytiscus evidently knew him as his 

 natural victim. Whenever he came in view he swam eagrrly toward 

 him. About the third circuit he succeeded in grasping him, and 



* Cope, in his synopsis of the Cyprinidae of Pennsylvania, has only seen this species 

 from the slope of the Alleghanies. It is a common form in the tributaries of Lake 

 Michigan. 



