; 
THE DEVELOPMENT OF THE OYSTER. 
BY W. K. BROOKS. 
EXPLANATION OF THE PLATES. 
Unless the contrary is stated the figures are drawn with a 
magnifying power of 250 diameters ; Zeiss. F. 2, but it was 
necessary to amplify the sketches considerably in order to re- 
produce, by the process of photo-engraving, the features 
which this magnifying power rendered visible, and the figures 
as they are reproduced are of about twice the diameter of 
camera sketches made with the same magnifying power. 
The first thirty-two figures show the process of segmenta- 
tion. Figure 1 is an egg at the end of the first period of rest ;; 
Figures 2, 3, 4, 5, 6 and 7, the changes during the first period! 
of activity; Figures 8, 9, 10, 11, 12 and 13, the changes dur- 
ing the second period of rest ; Figures 14, 15 and 16, those* 
which take place during the second period of activity ; 17, 18- 
and 19, those which take place during the third period of rest ;; 
20 and 21, during the third period of activity ; 22, during the 
fourth period of activity ; 23, during the fifth period of ac- 
tivity, and the remaining figures show more widely separated 
stages. In all the figures of segmentation, except 29, 30 and 
31, the formative pole is above and the nutritive pole below. 
