4 BULLETIN 273, U. S. DEPARTMENT OF AGRICULTURE. 



ingly small size, he contends, makes them physically inadequate to 

 sustain the caterpillar in the air. On the other hand, the very numer- 

 ous, very long hairs which cover the larva, in addition to the wonder- 

 ful amount of silk it is capable of spinning, point to the general 

 morpho-physiological structure as the factor enabling it to soar. 



He compares this ability of the caterpillar with the meaning of 

 soaring as this term is used by V. N. Chitrovo in an epoch-making 

 botanical work on the study of weeds. 1 Soaring is the capability of 

 a body passively to participate in an air current, as if constituting 

 part of it, arising from special characters in the structure of the body. 

 The analogy in function between the wind-borne seed and caterpillar 

 is complete. 



Soaring is determined by the coefficient calculated by the following 

 formula : 



c _ /(cm 2 ) 

 w(gr) 



where C is the soaring coefficient; /, the surface area (in square cm.); 

 and w, the weight (in grams) of the caterpillar. The coefficient of a 

 bare, freshly hatched first-stage caterpillar is 514.285 and Shcher- 

 bakov says that it would be more than six times as great if the area 

 of the hairs were included. 



Compared with the Chitrovo soaring table of seeds, the coefficient 

 for the first and second stages of the caterpillar places them among 

 the greatest seed soarers. In a slight wind these caterpillars are 

 capable of soaring. The distance they can cover depends on the 

 topography of the country, the character and abundance of vegeta- 

 tion, the mobility of the caterpillar which in turn depends upon the 

 temperature of the atmosphere, and the availability of foods. The 

 soaring coefficient diminishes sharply for caterpillars in the second 

 stage. 



This investigator also states that G. G. Jacobson once, while trav- 

 eling, observed caterpillars flying in masses toward him, despite the 

 fact that he was at least 17 miles away from the nearest forest. 



STUDIES OF STRUCTURE AND FUNCTION OF ACUMINATE AND VESICU- 

 LAR HAIRS. 



Owing to the differences of opinion existing as to the structure and 

 function of the hairs covering the bodies of first-stage larvae, the 

 writer and Mr. C. E. Hood, with the assistance of Dr. J. W. Chapman, 

 made some tests during the winter of 1914-15. The aim of these 

 experiments was to study both the long acuminate hairs and the short 

 ones bearing vesicles. As the results differ somewhat from those of 



1 Atlas von Samen und Friichten der Feldunkraiiter aus Mittelrussland. Bui. fur angewandte Botanlk, 

 wissenschaftliches Organ des Bureau fur angewandte Botanik (Monatsschrift), Jahrg. 7, no. 3, 118 p., 16 

 fig., 13 pi., March, St. Petersburg, 1914. 



