10 BIOLOGICAL SURVEY OF 



Further development is shown in figure 5 (from older veil) ; 

 growth of posterior end of body ; intestine outlined by pigment ; lens 

 vesicle visible. The heart beat begins at about this stage. 



July 1st, second day of development (fig. 6). Temperature, 10 a.m., 

 14.2°C.; 7 p.m., 13.0° to 13.8°C. 



Further development of intestine shown hy the line of pigment 

 along its sides ; optic and lens vesicles well defined. 



Later in the day, some of the embryos hatched (fig. 7). Length, 

 2.44 to 2.52 mm.; yolk sac, 1.58 to 1.62 mm. in diameter; heart and 

 pericardial cavity very large; brain a single only slightly differ- 

 entiated tube. 



July 2nd, third day of developynent (fig. 8). Temperature, 10.30 

 A.M., 14.5° to 15.0°C. 

 Cerebral vesicles well differentiated ; eyes and heart now relatively 

 smaller; diffuse pigment in posterior end of body. 



July 3rd, fourth day of development (fig. 9). Temperature, 9.30 

 A.M., 16.0° to 16.5°C. 



Cerebral vesicles further developed ; eyes strongly pigmented ; 

 pectoral fins present. 



The lateral view (fig. 10), a few hours older, shows the large head 

 and its contour due to the mesencephalic flexure and the large cerebral 

 vesicles; also position of the pectoral fins and the simple, slightly 

 convoluted intestine. A considerable amount of yolk absorption has 

 taken place; pigmentation is well advanced on the anterior part 

 of the neural tube, under the notochord and on the dorsal side of 

 the yolk sac. 



July 4th, fifth day of development (fig. 11). Temperature, 10.30 



A.M., 16.0° to 17.0°C. ; the water was cut off a short time during 



the day. Temperature at 5.30 p.m., 20.5°C. 



Eapid increase in size and length of body ; more rapid growth of 



intestine is shown by its increased convolutions ; pigment of posterior 



end of body shows a tendency to differentiate into three bands; a 



shallow notch dorsally behind the head has appeared in the broad 



thin fin which encircles the whole body in the sagittal plane during 



the larval stages ; pelvic fins behind the pectorals on the yolk sac 



near the body. 



July 5th, sixth day of development (fig. 12). 



A slight protuberance at the bottom of the dorsal notch (begin- 

 ning of the great dorsal ray) ; cartilages around the mouth begin- 

 ning formation; pigmentation of posterior end of body in three well- 

 differentiated bands ; yolk absorption well advanced. Larvae 4.5 to 

 5.1 mm. in length. 



