66 William B. Herms 



smallest piece had eaten it clean and had migrated, while almost 

 all larvae on the larger pieces continued feeding until about noon 

 of August I (67 to 72 hours feeding) when practically all migrated. 

 A few, however, continued feeding on the unconsumed flesh and 

 the last larva did not migrate until after noon of August 3. 



That the larvae on the last two pieces of fish did not continue 

 eating until the flesh was consumed, indicates that there is an 

 optimiun when enough nourishment has been taken to pass through 

 the metamorphosis to best advantage, and at this point migration 

 takes place. That this optimum is not always reached is shown 

 by the early migration because of food shortage, and this does 

 occur at times out of doors, since eggs and larvae may be deposited 

 in such large numbers on a single fish that an early migration is 

 necessary. Thus we have sharp competition which is further 

 augmented by the pressure of four species, each more voracious 

 than the other if that were possible. There has been, undoubtedly, 

 a gradual adaptation in the past to the existing conditions. In 

 order that the flies might exist in the locality, there must have been 

 a conformation to the food supply, /. e., a race of flies which can 

 adapt itself to an inconstant, somewhat periodic supply of food 

 would survive. Further there must have been an adaptation of 

 the four species already mentioned to each other, a species which 

 required a comparatively long feeding period could not well exist 

 with a species whose feeding period was of short duration. The 

 food would invariably be consumed by the quick feeder, while 

 the former would suffer starvation. As it is, all larvae migrate at 

 about the same time, /. e., when the fish is consumed which usually 

 requires a fairly uniform time, as above noted. A glance at the 

 larvae at this time will reveal the fact that there are two general 

 sizes of larvae present, very large ones and small ones. All have 

 fed during approximately the same time, yet Sarcophaga sarra- 

 ceniae has attained its enormous size while Lucilia caesar is uni- 

 formly smaller. The greatest variation in size is found in the 

 former. The larvae of the screw-worm fly are usually smaller in 

 average than Lucilia caesar. 



There is probably also a correlation with the surf producing 

 storms, which is discussed in full later in this paper. Another 



