84 CONK LIN. [Vol. XIII. 



terminal ; the basal cells were produced by the second division 

 of the apical cells (the turret cells were formed at their first 

 division), and, as just explained, the terminal cells are derived 

 from the second group of micromeres. (See Diagram 6.) 



(b) Axial Relations. — When first formed the centre of the 

 cross lies exactly at the animal pole of the &g^, and the polar 

 bodies are attached at the point where the four apical cells 

 meet. The arms of the cross lie between the first and second 

 cleavage furrows, about 30° or 40° to their right, i.e., in a 

 clockwise direction from those furrows, Figs. 29-32. 



At the period when the three smaller entoblasts are formed. 

 Fig. 33 and Diagram 7, the whole ectoblastic cap is rotated to 

 the left until the arms of the cross come to lie nearly over 

 those furrows, so that one arm is approximately anterior, one 

 posterior, one right, and one left. This is not strictly true, 

 since it can be seen by consulting the figures that even after 

 the general rotation of the ectoblast shown in Fig. 33 the arms 

 of the cross do not lie in the furrows between the macromeres, 

 but slightly to the right of them. This continues to be true 

 up to a late period in the cleavage, e.g., in Figs. 51 and 53, the 

 left arm of the cross is distinctly farther forward than the 

 right, while in these figures and a great many others, e.g., 

 Figs. 64, 65, 6Z, 71, 72, 75, and 76, the anterior arm, which 

 has now grown around to the ventral side, lies to the right of 

 the mid line of the embryo. Ultimately, however, the anterior 

 arm, which can be much more easily followed than the others, 

 comes to lie precisely in the median plane. Figs. 79, 81, 82. 



By another and much greater shifting of the ectoblast, which 

 will be described in another section, the entire cap of ectoblast 

 is carried forward through an angle of about 90°. This forward 

 shifting goes on at the same time that the ectoblast is rotating 

 in an anti-clockwise direction, so that by the time that the 

 anterior and posterior arms lie in the median or second furrow, 

 which can still be plainly seen between the yolk cells, the 

 transverse arms lie anterior to the transverse or first furrow. 



From its earliest formation up to a late stage in its history 

 the cross in itself is distinctly dexiotropic ; i.e., each arm taken 

 in connection with the apical cell from which it is chiefly 



