284 A - RICHARDS. 



EXPLANATION OF PLATE I. 



These figures were all drawn with the aid of a camera lucida and Leitz two mm. 

 objective with twelve compensating ocular (except figure sixteen as noted below). 

 They are reproduced here at a magnification of a little more than eighteen hundred 

 diameters. 



FIG. i. F9 X FcT normal; fifth cleavage division. Metaphase plate of which 

 the chromosomes of two levels only are shown. Stage of maximum condensation 

 of chromosomes. 



FIG. 2. F9 X CcT Both radiated for three minutes before feitilization; 

 second cleavage division. The beginning of chromosome division and first signs 

 of separation of chromosomes are shown in this part of metaphase. 



FIG. 3. F9 XCcf; eggs radiated for fifteen minutes before fertilization; 

 second cleavage division anaphase. The loosely formed chromosomes show in- 

 creased size, the linin membrane and the chromosomes. 



FIG. 4. Fc? X Cc?; sperm radiated for fifteen minutes before fertilization; 

 second cleavage division; chromosomes in similar condition to Fig. 3. 



FIG. 5. F9 XCcf; sperm radiated for three minutes before fertilization. 

 The beginning of the vesiculation of the chromosomes. Liquid is being taken 

 into the linin sac which in consequence swells up. A few of the chromosomes 

 from both ends of the anaphase spindle are shown. 



FIG. 6. F9 X Ccf; eggs radiated fifteen minutes; from one pole of anaphase 

 of second cleavage. Same process carried farther. 



FIG. 7. F9 X Ccf ; both radiated three minutes; third cleavage division. A 

 section through one pole of anaphase. All chromosomes are vesicles, showing no 

 fusion, no condensation. The swelling process is still proceeding. The arrow 

 points to the position of the sphere. 



FIG. 8. F9 XCd"; both radiated three minutes; fifth cleavage division, 

 telophase. A somewhat oblique polar view. Nuclear division completed, but 

 cytoplasmic not yet fully accomplished. Chromosomal vesicles further swollen, 

 but quite distinct. 



FIG. 9. Same material as Fig. 8. Telophase from one end of an incompletely 

 divided fifth cleavage spindle. A so-called "reconstruction stage," with no sign 

 of fusion of vesicles. 



FIG. 10. Same material and stage. The aster at the right end is drawn in 

 position from next section. The distinctness of the chromosomal vesicle at the 

 side is particularly to be noted. 



