BIOLOGICAL SUEVEY OF 



other; they contain a fluid which is apparently water, or 

 possibly a thinner mucus. The eggs in the veil of the earlier 

 stage of development measured 1.61 to 1.84 mm. in diameter. 

 They were nearly spherical. The eggs of the older veil were 

 slightly prolate, and became progressively more so along the 

 diameter parallel with the body axis as the body of the embryo 

 developed, as is shown by the following measurements. When 

 first taken into the laboratory, on June 29th, the eggs of the 

 older veil measured on the short diameter 1.56 to 1.63 mm.; 

 along the long axis, 1.61 to 1.86 mm. Just before hatching, 

 on July 1st, eggs of the same set measured 1.72 to 1.74 mm. 

 on the short diameter, and 1.79 to 1.94 mm. on the long axis. 



The embryos hatched in large numbers in an apparently 

 normal manner; the eggs of the older set began to hatch on 

 July 1st; those of the younger veil about a day later. The 

 larvae thrived and grew at a rate slightly less than a milli- 

 meter in length for five or six days ; then growth slowed down 

 and stopped. From about July 8th to July 12th there was 

 no increase in length; during this period the larvae began 

 to die ; all had disappeared on July 13th. 



On July 7th, the larvae were swimming about, being dis- 

 tributed evenly on the surface. Later on the same day, they 

 were seen to be endeavoring to swing toward the bottom and 

 all were almost upright. The morning of July 8th found 

 them all swimming head downward with large numbers about 

 3 inches below the surface. At 5 p.m. almost all were swim- 

 ming about the jars at all levels and every fish with its head 

 downward. On July 9th, in the morning, the majority of the 

 individuals were near the bottom and very few were in the 

 upper half, except those still remaining on the surface, prob- 

 ably held by the scum from the veil. In some cases a tendency 

 to swim downward toward the side from M^hich the light came 

 was noticed. The 10th and 11th found conditions the same, 

 and on the 12th they died very rapidly. 



Great difficulty w^as experienced in keeping the fish in the 

 tanks as soon as they hatched, for they would either float over 

 the top or get drawn against the strainers, M^hich would kill 



