248 



HRNKST E. JUST. 



by glass rods as well as the open watch glass were used throughout 

 the next series of observations. 



Slides ii4th Glass Support for Cover Slip. 



Four or five eggs on a slide were watched continuously through 

 the first cleavage, the indicator used merely to point out quickly 

 the point on the membrane where the sperm was attached. Very 

 few sperm were used in these observations, obtained through 

 diluting several times the water which contained them. These 

 observations were repeatedly made at night and at different 

 times during the day. Some of the eggs failed to show the indi- 

 cator and to develop. In all that segmented, the first cleavage 

 plane passed either directly through the entrance-point of the sperm 



FIG. 10. First cleavage. 



or a degree or so from it, with the indicator parallel to the cleavage 

 furrow (Fig. 10). It is possible, as stated above, to keep the 

 spermatozoon in view after the amceboid stage until it disappears 

 within the egg. The middle piece is left without. With the aid 

 of the middle piece, the character of the membrane at the en- 

 trance point (Fig. 7), and the oil drops near, it is possible ab- 

 solutely to hold in view the exact spot at which the sperm was 

 engulfed. 



At intervals of two to three minutes, seven slides with very 

 few eggs on each were prepared. Sperm was added and after 

 a minute the eggs covered and every precaution taken to avoid 



