178 FRANK W. BANCROFT 
30 
Fig. 28 F. majalis egg hybrid, four days old. Shows position of the heart 
which has just begun to beat, and the shallow vesicle, V. underneath the embryo. 
Fig. 29 Pure F. majalis, four days old. Same series and age as embryo in 
fig. 28. To show the greater depth of the vesicle, V. under the embryo and the 
normal position of head and heart. Heart has just begun to contract. 
Fig. 30 F. majalis egg hybrid, twenty-four days old. Dissected out of the 
egg shell at a time when a few fish of the same lot had hatched and when many 
had died. Shows vesicle V. under the embryo and the greatly stretched heart 
within it. 
