ORIGIN OF VASCULAR TISSUES 95 



In figure 50 are shown two lacunae dorsal and mesial to the 

 optic cups. Their red color could no longer be distinguished 

 four hours after this figure was made. Figures 51 and 52 are 

 sketches of the dorsal cephalic surface of an embiyo the history 

 of which is given in greater detail in a previous publication (53, 

 p. 103). At its four-cell stage the ovum was placed in a solu- 

 tion of 50 cc. sea water containing 10 cc. of yV molecular bu- 

 tyric acid, where it remained for twenty-four hours. It was then 

 placed in running sea-water. On the ninth day a blood lacuna 

 was observed over the left eye (fig. 51). Sixteen hours later this 

 lacuna could not be seen, but another located symmetrically 

 with its former position was observed on the right side. WTien 

 the embryo was sectioned, eosinophilous areas corresponding to 

 both these lacunae were found in section. The explanation of 

 these circumstances is rather difficult. It seems unlikely that 

 the hemoglobin should leave a cell unless it should disintegrate. 

 It may be that the overlying mesenchyme rendered the first 

 lacuna invisible. Figures 53 to 56 need not be further discussed. 

 They merely show the position of others of the lacunae which 

 were observed in this anterior region. While the location of the 

 smaller groups, and especially that of the single isolated eryth- 

 rocytes is rather indefinite, there are certain regions rather char- 

 acteristic for erythrocyte-formation. 



Figure 56 shows a very exceptional condition. No case simi- 

 lar to this was found in the entire series of experiments. In 

 this instance, the posterior portion of the embryo was the part 

 affected ; as a result it is diminutive in size. The anterior end is 

 relatively normal. Correlated with these conditions we have 

 discontinuous lines of erythrocytes extending into the ophthalmic 

 region, which were not carried there by heart-pulsation. The 

 rudimentary posterior end contains no erythrocytes. 



Figure 58 shows a side view of an embryo which, at the four- 

 cell stage, was treated with a mixture of equal parts of 4 per 

 cent alcohol (sea- water solution) and a solution made from 2 cc. 

 of Too per cent KCN in 50 cc. sea-water. The embryo developed 

 without a circulation. The heart possessed solid extremities. 

 On the twelfth day a longitudinal column of erythrocytes could 



