150 ETHEL BROWNE HARVEY. 



admission of air. Instead of dividing into two, frequently 

 several asters appear (Figs. 9, 21, 28) and the egg divides quite 

 irregularly. Sometimes one fairly large cell divides off (Fig. 10), 

 sometimes several large lobes start to constrict off (Fig. 22), 

 sometimes many very small fragments pinch off (Figs. 27, 28, 

 32, 33)- Sometimes the constrictions complete themselves and 

 form cells, sometimes they again fuse with the main cell body. 

 The following stages are likewise irregular, the cells seeming to 

 attempt all sorts of methods of righting themselves by trying 

 first one plane and then another, meanwhile obliterating a plane 

 already in existence. 



These eggs seemed so abnormal in appearance that I at 

 first threw them aside thinking that they had been harmed by 

 some experimental conditions and that they were about to die. 

 But much to my surprise, I found that many living larvae were 

 present in some of the chambers one morning. I have since 

 watched many individual eggs pass through these most amazing 

 stages, assuming the most bizarre appearance, cells of all sizes 

 pinching off and again fusing in the most irregular fashion. 

 But these same eggs succeed in righting themselves, and finally 

 give rise to a number of equal cells, and go on with a regular 

 cleavage resulting in normal blastulse. Stages in the develop- 

 ment of four such eggs are given in Figs. 7-18, 19-23, 24-31, 

 32-35. Even a very short exposure to the absence of oxygen 

 (5 minutes) is sufficient to call forth these peculiarities when 

 air is readmitted. A long exposure at any other stage previous 

 to the full metaphase does not give this result. 



If the cell has elongated preparatory to division after being in 

 the chamber for about twenty minutes, that is, during absence of 

 oxygen, if kept longer in hydrogen, it will again round out and 

 if a division plane has started as it sometimes does, it will again 

 become resorbed (Figs. 36-38, 39-41). In many cases a division 

 plane has started to come in after the egg has been in the chamber 

 30 minutes, more than time for all the oxygen to have gone, 

 and after the blue color of the methylene blue has gone but 

 before the mitotic figure has faded out, but this is resorbed if 

 kept in hydrogen. On readmission of oxygen, these eggs proceed 

 with the same sort of irregular cleavages as those in the full 

 metaphase, but result finally in normal blastulae. 



