286 WATASE. [Vol. IV. 



anterior half of the blastoderm, and the latter are derived from 

 the original posterior segments. 



The nuclei in the central segments are decidedly in different 

 stao-es of growth. Those in the anterior segments are far more 

 advanced than those in the posterior segments. The outlines 

 of the anterior central segments present interesting points for 

 study. 



In the first place, we see that the shape of a given cell is 

 determined by the condition of the environment ; that is, it con- 

 forms to the space determined by the meeting of several other 

 sesfments. The lateral horn on the outer border of each cell 

 fits into the space between the heads of two marginal segments. 



On the other hand, the same cell appears to me to offer 

 another example of how the outline of a given cell may arise 

 from another cause. For instance, the conical process at the 

 anterior border of the same cell, penetrating into the substance 

 of the marginal cell is produced by a different cause from that 

 producing lateral horns already referred to. The anterior horn 

 came into existence in connection with the production of the 

 caryokinetic phenomena going inside of its cell boundary, and 

 has some intimate connections with the archoplasmic sphere 

 which lies nearest to it. 



Fig. 25 represents the blastoderm at the twenty-two cell stage. 

 The number of the marginal cells is twelve — the number we 

 had in the preceding stage. The inner cells have been increased 

 to ten from the four previously present. The history of the 

 two pairs of inner cells of the previous stage (Fig. 24) is again 

 repeated in the present stage. The two anterior segments 

 which were further advanced than the posterior pair in Fig. 24, 

 have nearly completed the division, and the posterior pair which 

 were in a resting condition are in pretty well advanced stages 

 of caryokinesis. 



The right segment is, however, a little further advanced than 

 the left segment. Two posterior marginal segments in direct 

 contact with the two inner cells above described also show that 

 the right segment is further advanced than the left one. The 

 segments between second and fourth furrows of cleavage in the 

 posterior half of the blastoderm, lying on the right and left side 

 respectively of the two inner segments above described, show 

 also difference in the degrees of division, the right half being in 

 advance to that of the left. 



