MORPHOLOGY OF TKLEOSTEAN HEAD SKELETON. 593 



Fig. 56. — Diagrammatic sagittal section tliioiigii ilic liead region of a 

 si.\th-day embryo of G aster est eus aculeatus ; killed within the egg. X 80. 



Fig. 57. — The same ; killed after being released from the egg. x 80. 



Fig. 58. — Diagrammatic sagittal section through the head region of a just- 

 hatched larva of Gasterosteus aculeatus of the ninth day. The doited 

 outline represents parts belonging to an eightli-day embryo which was killed 

 within the egg. X 80. 



Fig. 59. — Diagrammatic sagittal section through the head region of an 

 adult of Gasterosteus aculeatus. x 6. 



Fig. go. — Dorso-lateral view of the trabecular and quadrate portions of the 

 head skeleton of a larval Amia calva, 19 mm. long, x 8. 



Fig. 61. — Projection of the cliondrocraiiial roof of a larval Salmo salar, 

 20 mm. long. X 20. 



Fig. 62. — Projection of the chondroeranial roof of a larval Salmo salar, 

 25 mm. long, x 17. 



Note. — Figures 1 — 16, 40, 47, 60, were taken from wax models. In all 

 except Figs. 47 and 60, the uiicoloured portions represent pro-cartilage; those 

 coloured blue, cartilage; those coloured green, ossifying cartilage; those 

 coloured yellow, bone without cartilage. 



