GREGORY: FISH SKULLS 



323 



the spiny rays of the dorsal fin? Why are all the little spikes on the top of the skull (Fig. 

 203) similarly dense and horn-like? Very possibly because spikes may result from the 

 dense crowding, near the center of growth, of rapidly proliferating tissue in which the 



ppipt ffa 



sphot pl^o:.:. 



lamysfes S. pluiTiieri 



Fig. 201. Scor-pana plvmieri. A. Side view. B. Occiput. After Allis. 



inelastic outer layers tend to inhibit or restrict the expansion but not the multiplication 

 of the inner layers. While these surface phenomena no doubt reflect obscure and deep- 

 seated molecular activities, it is worthy of note that a hom-like texture of originally bony 



17 



Fic. 202. SehasUs mannns. Left opercular bone enlarged. 



