PHYSIOLOGICAL PROBLEMS IN THE LIFE- 

 HISTORIES OF ANIMALS WITH PAR^- 

 TICULAR REFERENCE TO THEIR 

 SEASONAL APPEARANCE 1 



PROFESSOR VICTOR E. SHELFORD 

 University of Illinois 

 I. Introduction 

 The fact that plants flower, fruits ripen, insects appear 

 and disappear in succession throughout a growing season 

 needs no statement even to the savage huntsman or the 

 city flat dweller. The variations of the usual succession 

 of appearances with peculiar seasons, unusual weather, 

 etc., are general guides to many operations of primitive 

 agriculture and matters of comment by all out of door 

 people. Seasonal succession has long been scientifically 

 investigated (see Alee, 11; Forbes, '16; Harvey, '08; 

 Hough, '64; Johnstone, '08; Shelf ord, '13). Only re- 

 cently has careful investigation of it been stimulated by 

 the general interest in modern ecology and economic prob- 

 lems. The importance of a knowledge of delayed germi- 

 nation of seeds to the agriculturist (Crocker, '06) has 

 further stimulated work along a line throwing light on the 

 general subject. The analysis of the physiological causes 

 of the normal succession of biological events in any season 

 calls on many of the laws of biology to formulate merely 

 the outline or even a portion of a life history, as, e. g., the 

 answers to questions such as why potato beetles appear 

 from hibernation at a certain time, and not earlier, and 

 deposit eggs on plants of the genus Solatium. Further, 

 as soon as we concern ourselves with the analysis of the 

 causes of the irregularities of appearance in any season, 

 the evident complication of problems is such that one may 



