290 



WATASE. 



[Vol. IV. 



Figs. 24 and 27, PI. XI, show two stages of cleavage. All 

 the blastomeres in front of the second cleavage furrow (2-2) 

 are more advanced than those lying behind it, as shown by the 

 stages of the caryokinetic figures. The nuclei in the posterior 

 half of the blastoderm shown in Fig. 27 are all in the "resting" 

 condition, while all of those in the anterior half have advanced 

 as far as the equatorial plate stage. The same fact has been 

 observed by Vialleton, in Sepia. If I represent the condition 

 in a diagram, and reduce back all the segments to the original 

 blastomeres from which they have sprung, it will be something 

 like Fig. XVI. 



xr. 



.VIMI. 



.XVIII. 



xix. 



i % ^ 



Fig. XIV. — The unsegmented blastoderm of the squid, showing the eccentric 

 position of the nucleus «; A, anterior; P, posterior; L, left; R, right. 



Fig. XV. — A diagram showing the one-sided development of the blastoderm. 

 The segment / gave rise to all the segments in the left half of the blastoderm, such 

 as are shown in Figs. 28, 30, 32. 



Fig. XVI. — A diagram showing the unequal cleavage in the anterior and the 

 posterior halves of the blastoderm. All the segments showing the more advanced 

 stages in caryokinesis such as are shown in Figs. 24 and 27 were descended from the 

 two anterior segments a. I. and a.r. 



Fig. XVII. — A diagram showing precocious cleavage among the descendants of 

 one segment, p.r. 



Fig. XVIII. — A diagram showing the seats of abnormal (triple) caryokinesis, on 

 the corresponding sides of the ovum, /./.', /.?•.' 



Fig. XIX. — A diagram showing the original segments, «./.', a.r.', from which 

 a pair of fused areas on both sides of the blastoderm (Fig. 29, PI. XII) were 

 descended. 



