THE DEVELOPMENT OF THE SQUID. 



375 



power. They are, as yet, entirely absent from the ante- 

 rior surface of the mantle. 



About this time small polygonal areolations, much like 

 epithelial cells, begin to make their appearance on the 

 posterior surface of the mantle, and soon spread over the 

 whole mantle, except the middle line of the anterior sur- 

 face, as shown in the figure. At a later stage (Figs. 201 



FIG. 200. 



FIG. 200. A somewhat older embryo, seen from the right side. The 

 external yolk is now so large that only part of it is shown in the figure. 

 (Drawn from nature by W. K. Brooks.) 



a', a", a"', ''". The four arms of the right side. /. The fin. g. The 

 gill. }>. The branchial heart, in. The free edge of the mantle, nc. The 

 neck cartilage, si. The siphon-tube, si". The lateral chamber of the 

 siphon, v. The valve of the siphon, x. The space between the integu- 

 ment and the surface of the external yolk, y', y,'y''', y'''. The four 

 divisions or regions of the yolk. 



and 202), they cover the head and arms, as well as the 

 mantle, and still later they make their appearance upon 

 the surface of the siphon. 



Upon cursory examination, they resemble epithelial cells 

 so much that they might readily be mistaken for them ; 

 but when more carefully examined with a high power, 



