EFFECTS OF CARBON DIOXIDE ON EGGS 359 



portions have the normal cUimped or himped appearance which 

 precedes diminution (compare fig. 2d with fig. 9). 



In rare cases, both the Si and the Pi cells were dividing at the 

 same time (fig. 3). When this occurred, the chromatin of the Si 

 blastomere showed the fused condition, while the chromosomes 

 of the P] cell were normal. 



In the 2-cell stages with the nuclei in the resting phase, no 

 departures from the normal could be distinguished. 



When the eggs are allowed to develop a short time before they 

 are preserved, the Pi blastomere begins to divide. The elon- 

 gated chromosomes, so characteristic of the primordial germ cells, 

 are always found and aside from the axis of division, the cell 

 appears normal. Here and there a tendency for the four chro- 

 mosomes to break up has been noted (text fig. J and L), but 

 this is not to be regarded, I think, as an effect of the CO2. The 

 point will be taken up in detail later under the heading 

 'Anomalies.' 



If the eggs are allowed to develop further until half are in the 

 4-cell stage, a variety of conditions are found in the 4-, 3- and 2- 

 cell stages. Needless to say, these various conditions arise out 

 of the 2- and 3-cell stages described above. 



Among the 4-cell stages we find three different types of em- 

 bryos. One of these (fig. 5) is perfectly normal, both in the 

 position of the blastomeres and in their nuclear conditions. A 

 second type is characterized by the failure of the four blasto- 

 meres to form a rhombus, as they normally should do (fig. 4).^ 

 Most frequently the planes connecting the two pairs of blasto- 

 meres lie at right angles to one another, but this is variable, 

 every imaginable condition being met with in a large number of 

 eggs. The third type is one where, in addition to an abnormal 

 position of the blastomeres, we find an unequal distribution of the 

 chromatin between the A and B blastomeres (fig. 6 ; this drawing 

 is of a 3-cell stage, selected because it shows particularly well the 



•* It is not to be thought that these various positions which the A and B blasto- 

 meres occupy are just phases of the normal shifting which certain cells of the egg 

 undergo about this period. As will be seen, these positions are retained in later 

 cleavage. 



