BUCKINGHAM. — DIVISION OF LABOR AMONG ANTS. 



433 



head was to place it as nearly as possible in a horizontal position for 

 the purpose of viewing its dorsal aspect. This was done in the case of 

 the transverse axis by placing the head so that the outer margin of the 

 two eyes was equally distant from the outline of the adjacent side of 

 the head ; in the case of the anterio-posterior axis, by bringing the an- 

 terior margin of the clypeus and the posterior margin of the head to 

 lie at the same focus. These two points can both be seen distinctly 





Figure 1. 



I ^o rsj fvj KJ rvj r^j 

 I C3 LP ^ U1 (=3 CA 



Figure 2, 



only when the head is in one position. In making the measurements 

 I used a Zeiss A* objective so set as to give a magnification of about 

 45 diameters at a projection distance of 430 mm. With this arrange- 

 ment the whole length of the head of the largest individual could be 

 covered by the ocular micrometer, by means of which the measure- 

 ments were made. To avoid accidental errors measurements were 

 taken more than once, and recorded in terms of divisions of ocular 

 micrometer. In all cases they were ultimately calculated in millime- 

 ters. By " length " is meant the distance measured in a straight line 

 in the median plane between the posterior margin of the head and the 



VOL. XLVI. — 28 



