56 J. H. Powers 



there were about fifty superb young broad-heads, such as those 

 shown in figures i, 3, 4, and 5, plate VIII. About one hundred 

 of the remainder were of similar type, though of smaller size, or 

 represented transitions between the common larva and the broad- 

 heads. Some of these transition specimens are shown in figures 

 6, 7, and 8, plate IX. The entire remainder of the larvae, al- 

 though varying in size from 5 to 1 1 or 12 cm., were very uni- 

 form in type. The muzzles were rather broad, but the head of 

 only normal width. All of the specimens had evidently lived 

 upon the bottom, feeding upon insect larvae. One of the largest 

 of the normal larvae is shown in figure 6, plate VIII ; with this 

 should be compared, not only the broad-heads, but figure 2 of 

 the same plate, which represents a free-swimming and somewhat 

 better fed specimen from an adjoining pond. The proportions 

 of these broad-heads were sufficiently remarkable, especially for 

 larvae which could hardly be more than eight weeks old ; and the 

 circumstances of their development, together with observations 

 made at the time of their capture or soon afterward, established 

 almost beyond a doubt the cause of their singular development, 

 viz., cannibalism. The overstocking of the reservoir, the lack of 

 the ordinary and adequate food supply, leaving the animals 

 crowded together upon the bottom, the clear water allowing 

 them to see and thus more readily attack each other, were ob- 

 viously favoring circinnstances. Then, too, in the course of an 

 hour's observation after the reservoir was sufficiently emptied to 

 permit of it, I observed three cases in which a broad-head was 

 holding or swallowing another good sized larva. Even within 

 the pails, to which these larvae were transferred from the net, a 

 number of broad-heads seized their companions immediately, 

 killing themselves as well as their prey in several instances, be- 

 cause, swallowing being a slow process, they could not rise for 

 air in the deoxygenated water of the pail. My aquaria, too, 

 showed interesting results at once. Every flat-head proved a 

 cannibal, while the ordinary larvae, as is usually the case, did 

 not, with very rare exceptions, attack each other in the least. 

 Ordinary larvae 10 cm. in length may, indeed, be starved to 

 death, or more frequently into metamorphosis, without their 



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