EVIDENCE OF GERM CELL SELECTION 401 



The next column, 'died in the shell,' shows the number of 

 embryos that failed to hatch. This included embryos of from 

 the first to the twenty-first day, but a considerable number of 

 them represent late stages, many having pipped without be- 

 ing able to escape from the shell. Since fresh eggs were put in 

 one or the other of the incubators every day, the temperature 

 could not be varied to meet the requirements of embryos in 

 late stages, and in consequence many chicks which were doubt- 

 less originally strong did not hatch. It will be appreciated 

 that the purpose of these experiments was not primarily to 

 produce viable chicks nor to test the vitality of eggs, but rather 

 to test the transmission of certain traits. To that end the main 

 effort was concentrated on bringing as many embryos as possible 

 to a stage where their peculiarities could be determined, the 

 number that actually hatched (last column) being a mere 

 incident. 



As indicated in table 2, a total of 1228 eggs were used, of 

 which 1100 proved fertile. From these 1100 fertile eggs there 

 were obtained in the manner just explained 808 embryos and 

 292 chicks. One hundred and ninety-four of the embryos 

 died before the end of the seventh day and were therefore use- 

 less for present purposes. This leaves 906 embryos and chicks 

 which yielded data of value. For all of these the presence or 

 absence of Polydactyly was recorded. Eight hundred and- 

 thirty-three of them reached at least the tenth day and fur- 

 nished data on brachydactyly. Finally, 721 developed suf- 

 ficient down so that their color could be determined. The 

 distribution of these traits in the subdivisions of the several 

 experiments is set forth in table 3.^ 



Table 3 summarizes all the pertinent data and calls for only 

 a brief explanation. It will be understood that the sum of the 



^ It seems unnecessary to extend this paper by the inclusion of the detailed 

 protocols which would fill a number of pages. Data for eggs laid each day were 

 recorded as well as the date and (known or estimated) age of every embryo that 

 failed to hatch. For the chicks that did hatch the measurements of each toe 

 were recorded, the index of brachydactyly determined and the grades of Poly- 

 dactyly and booting estimated. The data will gladly be put at the disposal 

 of anyone who may wish to make use of them. 



