PLATE 13 



EXPLANATION OF FIGURES 



49 to 57 Dorsal views of the cephalic portions of chemically treated embryos. 

 Figures 57 and 58 are lateral views. The stippled areas in these figures indicate 

 the location of erythrocytes as observed in the living embryo. 



49, 50, 53, 55 Represent the heads of fourteen-day embryos, which at their 

 four-cell stage were treated for twenty-four hours with a solution of 50 cc. sea- 

 water to which had been added 15 cc. of m/12 butyric acid. They are all from the 

 same e.xperiment, one-fourth of the embryos in which yielded similar results. 

 Owing to the evanescence of the red coloring, it is possible that many others 

 may have passed through this critical stage without being observed. 



51 and 52 Described with sufficient detail on page 95. 



56 and 57 From embryos obtained from the same experiment as that of 

 figures 43 and 44. 



58 From an embryo, the treatment of which is described on page 95. Erth., 

 er3'throcytes ; Ht., heart. 



59 Represents an embryo, only a small portion of the body axis of which 

 developed. No heart formation has taken place. There is a large dilated peri- 

 cardium in the region of which are many isolated erythrocytes. Embryo from 

 same experiment as that from which the embryos of figures 49, 50, 53 and 55 were 

 obtained. It seems improbable that the 'pericardium' of this embrj^o should 

 be interpreted as Kupffer's vesicle. Even so, there are blood cells of local origin 

 on what would then be the anterior yolk, not shown in this figure. 



60 Represents a case in which the embryonic body has failed to develop, or 

 as such has been transformed into mesodermal and vascular tissues which are 

 scattered entirely over the yolk. The embryo at the four-cell stage was treated 

 for ninety-six hours with a solution of 50 cc. of sea-water to which was added 

 15 cc. of a molecular solution of acetone. 



61 A lateral view of a twelve-day embryo treated for twenty-four hours 

 subsequent to the four-cell stage with a solution similar to that employed in case 

 of the embryos represented by figures 49, 50, 53, 55 and 59. Kindness of Dr. E. 

 I. Werber. 



156 



