3i6 Charles Zeleny. 



Some of the larvae are shown in Figures 15, 16 and 17, and it 

 will not be necessary to describe the individual cases in detail, as 

 the results are very definite and clear. The figures give charac- 

 teristic types of larvae developing from the upper quartet (Fig. 

 15), from the lower quartet (Fig. 16), and from lateral four-cell 

 groups (Fig. 17A, B, C). Figure 17D shows a case in which 

 six of the eight cells were represented, two of the lower quartet 

 having been destroyed. 



IX. Sixteen-cell stage. Five eggs of the sixteen-cell stage suc- 

 cessfully withstood an operation, and larvae from three of these 

 were studied. 



In one egg equal upper and lower portions were obtained by a 

 horizontal cut, but there was not a separate identification of them, 

 and they were placed in one dish. At forty-eight hours after fer- 

 tilization both resultant embryos were ciliated. They showed a 

 difference in that one had ragged edges and swam in a circle, 

 while the other had even edges and remained stationary. The 

 embryos were lost. 



In two cases the upper four cells were successfully separated 

 from the lower twelve. The two cases are taken up in turn. In 

 the first one the division was very clear without injury to any of 

 the cells. At forty-six and a half hours after fertilization the 

 upper four cells had 'formed a small distinctly outlined spherical 

 ciliated embryo, with no rotation or forward motion of the body. 

 There is a distinct blastocoele containing rounded cells, a large 

 apical organ and no enteron or lappets (Fig. 18C). At the same 

 time the lower twelve cells have formed a ciliated rotating embryo, 

 with a large solid archenteron entirely filling up the cavity of the 

 blastocoele. Neither apical organ nor lappets are present. The 

 two embryos thus show a very pronounced difference, the one 

 formed from the upper four cells containing an apical organ and 

 no archenteron, and the other, from the lower twelve cells, con- 

 taining an archenteron and no apical organ. 



In the remaining case the upper four cells were separated from 

 the lower twelve as before. One cell in the former was slightly 

 injured, but all the cells of the latter were left in good condition. 

 From the upper four cells at forty-six and a half hours after fer- 



