^36 H . H. N ewman 



pures taking an average of eighteen days to hatch, the H hybrids 

 an average of twenty days, M pures an average of twenty-six days. 

 No M hybrids hatched. 



The survivors of the three strains that hatched were placed in 

 balanced aquaria, were fed on clam juice, and generally carefully 

 looked after. The H hybrids throve in this environment and, 

 on the average, outgrew the H pures. About a dozen of these H 

 hybrids continued to live in the aquaria after all of the H and M 

 pures had died. The survivors were transferred to an aquarium 

 provided with a standpipe, so that they could have a continual 

 flow of fresh sea-water, with the abundant supply of minute 

 organisms that are found in it. The young fish grew rapidly on 

 this diet and lived for seven months. During this time they were 

 looked after by Dr. Sumner, to whom I take this opportunity of 

 expressing my thanks for his kindness. Only four of these young 

 fish survived until March, at which time they simultaneously 

 sickened and died. A comparison of these young fish with pure 

 bred specimens of about the same age and size reveals an inter- 

 esting resemblance to both parent species. There is so little 

 material on hand, however, that it is deemed wise to reserve a 

 treatment of the advanced conditions until a greater degree of 

 success in rearing the young has been attained. It seems in no 

 way impossible to rear the hybrids to maturity. 



Series 6, June ig, igo6. This series was started on the after- 

 noon of the same day as the last series. DiflFerent parents were 

 used and only ten specimens of each strain (selected after cleavage 

 had begun) were followed. In all important details this series 

 agreed so closely with Series 5, that it seems superfluous to record 

 the data. It was, in fact, the striking resemblance between these 

 two series reared under the same conditions, that suggested the 

 idea of controlling future attempts at equalizing the develop'mental 

 conditions of the embryos by equalizing the physiological condi- 

 tions of the adults. 



The six series above described are all that were studied in detail 

 through the whole or nearly the whole process up to the period of 

 hatching. Many other series, however, were started for other 

 purposes;* to furnish material for experimentation and preserva- 



