MOUNT DESERT REGION 11 



July 6th, seventh day of development (fig. 13). Temperature, 10.30 

 A.M., 16.5° to 17.5°C.; 3.45 p.m., 16.0° to 17.5°C. 



Pelvic fin has shifted its origin to side of body over yolk sac and 

 ventral to pectoral fin; pelvic fin greatly increased in length and 

 pigmented toward distal end ; mouth cartilages well advanced in 

 development ; otic vesicle visible. 



The shift in position of the pelvic fin along with the considerable 

 absorption of the yolk indicates that the yolk sac has become incor- 

 porated into the body and its walls are now definitelj^ a part of the 

 body wall. A conspicuous feature of the head of this stage is the 

 large mesencephalon (optic vesicles) — probably an expression of the 

 functional development of the eye-brain mechanism which soon comes 

 to be an essential in the capture of food when the yolk has been 

 absorbed. 



July 7th, eighth day of development (fig. 14). Temperature, 10 a.m., 

 16.5° to 18.0°C. 

 Chief features of this stage are the growth of the dorsal ray and 

 advance in development of mouth structures. Larvae 5.3 to 6.2 mm. 

 in length. 



July 8th, ninth day of development (fig. 15). Temperature, 12 m., 

 17.0° to 18.5°C. 

 Dorsal ray conspicuous ; mouth parts well developed ; mouth begins 

 to open ; 3'olk nearly absorbed ; origin of pelvic fin far forward ; 

 second band of pigment in middle of pelvic fin. Larvae 6.1 to 6.7 

 mm. in length. 



July 9th, tenth day of development (fig. 16). Temperature, 10.45 

 a.m., 19.5° to 21.0°C. 

 A second ray appearing behind the first dorsal ray; the posterior 

 part of the intestine and anus well differentiated ; growth of the 

 above-mentioned structures is apparently correlated with an increased 

 depth of the head and of the part of the body behind the anal region ; 

 a remaining trace of yolk visible. The relations of the fins and of 

 the dorsal ray are shown in figure 17. 



July 10th, eleventh day of development (fig. 18). Temperature, 

 11 a.m., 18.0°C. 

 A small spur has appeared on the ventral edge of the pelvic fin 

 near its base ; mouth open ; relations of fins, of dorsal spine and of 

 operculum are shown in figure 19. 



July 11th, twelfth day of development (fig. 20). 



Mouth structures well developed; spur at base of pelvic fin and 

 dorsal rays are longer. The dorsal view (fig. 21) shows the well- 



