and Laboratory Methods. 2013 



position for all objects except the most difficult, which may require the strong 

 central illumination. 



The system of condensers is of the utmost importance. The best combina- 

 tion for microscopic projection consists of three plano-convex condensers, each 

 four and one-half inches in diameter, and arranged as follows : No. 1 is double 

 thick lens of about five inches focal length with its plane side next to the light ; 

 No. 2 is a medium thick lens of six and a half inches focal length with its con- 

 vex side facing the convex side of No. 1, and enclosed in the same cell with it; 

 No. 3 is a thin lens of about eleven inches focal length, and is attached to the 

 water tank with its convex side facing the microscope. 



A simple plano-convex sub-stage condenser of if inches focal length is a 

 necessity in high power work with the above named condensers, but its efficiency 

 varies with its distance from the object. The correct distance for each object- 

 ive should be determined by experiment and recorded for reference. Begin the 

 test with the sub-stage condenser pushed up close to the object and slowly draw 

 it away. 



All the directions given for centering, adjusting and testing the working dis- 

 tances with the electric lamp apply equally well to the oxyhydrogen light, in 

 which the luminous point is constant, but the less intense light materially 

 reduces the maximum magnification. A. H. Cole. 



University of Chicago. 



LABORATORY OUTLINES. 



For the Elementary Study of Plant Structures and Functions from 

 the Standpoint of Evolution. 



A SERIES OF FORMS TO ILLUSTRATE THE EVOLUTION OF SEX. 



XVI. Eudorina elegans, Ehrb. 



Order, Protococcales. Family, Volvocaceae. 



Eudorina frequently occurs in pools of rain water, in ponds, and in marshes. 

 The colonies are hollow, free-swimming bodies, more or less spherical in shape, 

 usually consiaiing of thirty-two cells which are considerably separated from 

 each other. 



1. Mount a drop of water containing the organism and examine under low 

 power. Under high power draw a single colony, showing the arrangement of 

 the cells. 



2. Draw a single cell, showing the two flagella, the red eyespot, and the 

 chloroplast with a pyrenoid. 



3. Vegetative propagation. The individual cells divide into sixteen or 

 thirty-two new cells, and these escape as daughter colonies the same as in 

 Pandorina. Draw a colony showing daughter colonies, and describe. 



4. Sexual reproduction. The colonies are either unisexual or hermaphrodite. 

 Draw a colony showing antherida (spermaries), consisting when mature of plates 



