BULLETIN OF THE UNITED STATES FISH COMMISSION. 423 



embryos which are the subject of this paper was any abnormality ob- 

 served in the development of the eyes or optic vesicles. 



Now for the history of the progress of the experiment and the ova- 

 The latter were taken at one of the Potomac stations organized upon 

 the plan proposed by Colonel McDonald. They were impregnated on 

 the 9th of April at 7 p. m., and brought to the Armory on trays and 

 spread out on damp cloths by spawn-taker Jones. They were placed in 

 one of the McDonald jars on the morning of the 10th of April, but, un- 

 fortunately for the fullest fruitiou of our hopes, during the night, owing 

 to an accidental occurrence or to the meddlesomeness of some irrespon- 

 sible busy-body, too large a supply of water was turned on, causing the 

 largest proportion of the eggs to be thrown out by way of the escape pipe 

 of the jar. What were then left, amounting to jjrobably two or three 

 thousand, had to suffice for the material for this account of their de- 

 velopment. 



On the 11th of April, the temperature of the water wasoT^ Fahr. It 

 had been about the same or a little lower on the 9th and 10th ; the water 

 of the Potomac, from which they were obtained at Ferry Landing, was 

 on those dates as low as 48° Fahr. On the 12th, the thermometer in- 

 dicated a temperature in the hatching apparatus ranging from 50° to 

 510.5 Fahr. On the 13th, the temperature ranged from 51° to 52° Fahr. 

 This was the fourth day, and sketches taken from the eggs at this time 

 showed that the blastoderm was just about to close, a condition ordinar- 

 ily attained in a temperature of 74° Fahr., in somewhat less than 24 

 hours. On the 14th of xipril, the temperature was 52° to 53° Fahr. ; 

 on the 15th, 53° Fahr. ; on this, the sixth day, the tail began to bud out. 

 On the 16th, the temperature was the same as on the previous day, and 

 the tail had, by this time, the seventh day, grown to about one-third 

 the length of that of the jnst-hatched embryo. On the 17th, the tem- 

 perature was 53°.5 Fahr. ; on the 18th, 51°.5 to 52° Fahr. ; on the 19th, 

 53° to 53°.5 Fahr. ; development still normal. On the 20th, the tem- 

 perature ranged from 53° to 54°; on the 21st, 55° to 55°.5 Fahr., and 

 about this time, or on the twelfth day, the eyes began to show the first 

 signs of pigmentation, becoming a shade darker than hitherto, verg- 

 ing toward brown. On the 22d, the temperature of the water w^^s 50°, 

 falling to 55°.5 Fahr.; on this, tlie thirteenth day, a few began to hatch; 

 the eyes were now fully pigmented and normal in their development. 

 On the 23d, the temperature of the water was oij'^.5 to 54° Fahr. On 

 the 24th, the temperature was from 54° to 540.5 Fahr, During 

 the 23d and 24th days of April, the hatching continued, most of the 

 embryos having ruptured their inclosing membranes on the 24th of 

 April, or the fifteenth day of incubation. On the 25th, the temperature 

 ranged between 54°.5 to 55° Fahr., and on this date, or the sixteenth 

 day, a few of the ova still remained uuhatched. On the 2Gth, the tem- 

 perature was 55° Fahr., all of the ova were now hatched, and no ab- 

 normalities of any sort were noticed. The embryos, however, were for 



