No. 3.] STUDIES ON CEPHALOPODS. 291 



The first furrow of cleavage is indicated by (I'-i) ; and the 

 second furrow by (2-2) ; «./., a.r. represent the anterior blasto- 

 meres. All the cleavage segments in front of the line (2'-2) in 

 Figs. 24 and 27, showing the more advanced condition of caryo- 

 kinesis than those lying behind, were descended from these two 

 blastomeres a.l. and a.r., as represented in the diagram (XVI) ; 

 and all those segments showing the backward conditions in their 

 nuclear changes were derived from the two segments which lie 

 behind them. 



Fig. 25, PI. XI, shows another interesting variation. All the 

 four segments, which descended from one quadrant {p.r., Fig. 

 XVII) are further advanced than their homologues on the 

 opposite half, which have descended from the corresponding 

 quadrants on the opposite half. 



Figs. 28, 30, 31, 32, were all taken from the eggs of one and 

 the same squid. As the examination of caryokinetic figures in 

 each segment of the blastoderm will show, those segments lying 

 on the one side of the first cleavage furrow are more advanced 

 than those on the other, making exceptions of those few segments 

 which are found along the posterior half of the median axis. 



I cannot well describe the extremely slight differences shown 

 by different blastomeres in different parts of the blastoderm. 

 A glance over the figures and the comparison of different seg- 

 ments will show them far more clearly than pages of verbal 

 description. 



As I have stated already. Fig. 31 was taken from the same 

 lot of eggs as Figs. 28, 30, and 32. But it is the right side of 

 the blastoderm which shows a more advanced condition, and not 

 the left side, as in the others. I am inclined to believe now 

 that in this case, the blastoderm was mounted with the wrong 

 side up, and what appears as the right side in the figure belongs 

 really to the .left side of the animal. If such was the case, the 

 left-handed variation, as shown in the series of four stages. Figs. 

 28, 30, 31, and 33, becomes interesting, since all the eggs come 

 from one and the same animal. It is probable that this ten- 

 dency to vary in the same direction may be due to the same 

 hereditary characteristics inherited from the parent organism. 



Fig. 29 is an interesting example of what may be designated 

 as the analogous variation of both sides of the germ. Four seg- 

 ments on each side of the blastoderm show a curious phenom- 



