458 H. H. NEWMAN 



During the months of June and July all of these species are 

 spawning in the Woods Hole region and little difficulty is experi- 

 enced in obtaining abundant material for crossbreeding. The 

 most successful experiments were those in which insemination 

 was accomplished by the dry method. In this way it was possi- 

 ble to avoid exposing either of the sexual products to waters of 

 harmful concentration, for eggs were stripped from well dried 

 females into bowls containing no water and they were mixed 

 with fresh milk or macerated testis. After allowing a few min- 

 utes for the sperm to impregnate the eggs, water of the proper 

 kind was added and excess sperm washed out. It was found 

 best to rear the eggs of F. heteroclitus, F, majalis and Cypri- 

 nodon in sea-water and those of F. diaphanus in fresh water. 

 All thrive well in about 25 per cent sea-water, but do no better 

 than when the two kinds of natural water are used. Likewise 

 all four kinds of eggs thrive in fresh water, but the eggs of F. 

 diaphanus do not do well in natural sea-water, in which they 

 undergo various degrees of plasmolysis. 



No less than three crosses of each type were performed and 

 careful comparisons were made possible through the frequent 

 camera drawings of individuals and details. The illustrations 

 herewith published are taken from camera drawings which seem 

 to represent the most typical condition. The method of pre- 

 senting the data is as follows: A chronology is given for each 

 cross and beside it in an adjacent column are given the details 

 of synchronous stages in the development of the control or pure 

 bred eggs of the maternal species. Only such details are men- 

 tioned as seem of particular significance as diagnostic of relative 

 rates of development or types of inheritance involved. In order 

 that repetition may be avoided the chronologies for the recip- 

 rocal hybrids between F. heteroclitus and F. majahs are omitted, 

 and the reader is referred for the facts to the previous paper in 

 which these crosses were first dealt with (Newman '08). The 

 references to details of pigmentation are intended to be merely 

 suggestive, since the study of pigment inheritance forms a spe- 

 cial topic for subsequent discussion. 



