THE EGG. 9 



reaching the base, and above may terminate at 

 the edge of a saucer-like depression, which forms 

 the cap of the egg, as is the case in the Baltimore 

 (Euphydryas Phaeton) [Fig. 15] ; but everywhere, 

 with more or less distinctness, be- 

 tween these buttressing ribs, the 

 surface of the egg is broken into 

 quadrangular cells [see Figs. 9, 10, 

 etc.] by delicate cross -ridges, which 

 often increase in stoutness toward the main ribs, 

 and in their turn buttress them. In the echinoid 

 eggs [see Fig. 12] the surface is never ribbed, but 

 'covered with a heavy net-work of deep pits, 

 whose bounding walls are rather coarse and 

 rough. In these eggs, too, the rosette of micro- 

 scopic cells at the summit is situated at the bot- 

 tom of a very deep and narrow well, where they 

 can with difficulty be seen. Other shells, as in 

 the globular eggs of the purples (Basilar- 

 chia), have the same style of pitting ; 

 but the cell-walls, though high, are 

 thin, and at every angle emit a little 

 filament, which gives the egg a brist- 



FiG.15.-E-gof ,. * 



E.i P hydryasi>hae- ling appearance [Fig. 16]. In some, 

 the ribs and the cross-ridges are so 

 numerous and of so similar a prominence [Figs. 

 17, 18] as almost to make them resemble the net- 

 work of pits on less regular eggs ; while in 

 others, like the nearly globular eggs of our em- 



