352 GEORGE W. BARTELMEZ. 



found the relations shown in Fig. 4 it was clear that if the egg 

 were turned about the polar axis through 180 we would have the 

 usual axis angle for this bird, as 75 per cent, of her eggs had angles 

 between 65 and 85. Now if the normal orientation of the oocyte 

 had been accidentally inverted the latebra should be found nearer 

 the cloacal chalaza than the other (vide p. 334 supra). It was 

 poached, cut through the long and polar axes and the latebra 

 was found 1.3 mm. nearer the cloacal end of the long axis (toward 

 the pointed end of shell) the reverse of the usual condition. It 

 is always possible that the egg was not inverted until after it 

 had entered the "uterus" but before the shell had been laid 

 down (cf. Taschenberg, 1894, p. 308), but I am inclined to think 

 that had this happened the yolk would have been normally 

 related to the air space. The occasional birds' eggs as those of 

 Corvus frugilegus (Taschenberg, 1894) which have the pigment 

 wreath at the pointed end of the shell instead of the blunt end 

 should be examined with this point in mind (vide, p. 332 supra). 

 We may say then, with some degree of certainty, that in the 

 present case the ovum was inverted at or near the time of ovula- 

 tion. 



The other inverted eggs were studied in the same way but the 

 latebra could not be accurately measured since its boundaries 

 usually become hazy even before laying (see p. 334). However 

 this simple explanation will not suffice for any of the other 

 inverted eggs I examined. A consideration of Fig. 4 will show 

 that it can only hold when the head of the embryo lies in the 

 third quadrant, i. e., between 180 and 270. The axis angles of 

 the other seven inversions lies between 285 and 325 with the 

 head therefore in the fourth quadrant. If, in these cases, we are 

 to get the relations of embryo and long axis characteristic of 

 the bird we must turn the ovum through 180 about the long axis 

 and view the embryo from the vegetal pole as if the yolk were 

 transparent. Obviously this means a reversal of polarity. 

 There is a period in oogenesis when this might happen but I 

 do not tee how it could be demonstrated. At the beginning of 

 my "period of differentiation" namely, (1912, p. 286), when the 

 nucleus is nearer the center of the oocyte than at any other time, 

 it is possible especially in oocytes with the animal pole nearer the 



