THE DEVELOPMENT OF THE SQUID. 367 



set is obviously the product of the division into two of a 

 spherule like those of the set (c), formed by separation, 

 somewhat earlier, from the end of a pyramid. Inside this 

 set is another series (rf"), equal in number to the set (d r ), 

 and arranged like this set, in pairs along the radii which 

 end in the pyramids. Inside there is another set (d'"), of 

 the same kind, so that, as we pass inwards in the line of 

 each pyramid continued, we have the following series : 

 1. the pyramids; 2. one large spher- 

 ule (c); 3. two spherules (d'); 4. two 

 spherules (d") ; 5. two spherules (d'"}, 

 and so on. 



FHI. 19.']. View of the anterior surface of an 

 embryo about two days old. (Drawn from nature 

 by W. K. Brooks. ) 



Hi. Mantle. s. Shell area. si'. Lateral 

 siphon folds, e. Eye. y. Yolk. b. Growing 

 edge of blastoderm. 



In about two days the embryo is in the stage shown in 

 Fig. 193, and the positions of many of the organs of the 

 future squid are now indicated. The blastoderm has 

 grown down around the yolk, which is now entirely cov- 

 ered by it, except at the point (y), opposite the point where 

 segmentation began. The growing edge of the blastoderm 

 is marked by a ridge (b), which is ciliated. The em- 

 bryo is now bilaterally symmetrical, with reference to a 

 plane through the long axis, and the blastoderm has be- 

 come raised into a circular area, the mantle (w), at the 

 end where segmentation began. In an anterior view (Fig. 

 193), there is an elevated pad, the eye-stalk (e) on each 

 side of the body, and when one of these is seen in surface 

 view, a little pit, or invagination in its centre, will be 

 seen ; this is the chamber of the eye. Between the eye 



