CHAPTER XIX, 



BILATERAL SERIES continued. 



FURTHER ILLUSTRATIONS OF THE RELATIONSHIP BETWEEN 

 RIGHT AND LEFT SIDES. 



I. Variations in Segmentation of the Ovum of Loligo. 



The following facts, taken from WATASE 1 , are introduced in 

 further illustration of the mode of occurrence of bilaterally symme- 

 trical M eristic Variation. 



*720. Loligo pealei. In the blastoderm the nucleus is placed eccen- 

 trically, being rather nearer to the posterior pole, as shewn in Fig. 



(i.t: 



a.r.' 



2 2 



p.r. pV. 



FIG. 149. Diagrams illustrating variations in segmentation of a Squid. 

 (Loligo pealei). 



I. Normal uusegmented ovum. ?;, the nucleus eccentrically placed. A, anterior. 

 P, posterior. L, left. E, right. II, III, and IV. The shaded portions shew areas 

 in which in some specimens nuclear division was precocious. V. In the two 

 shaded areas triasters occurred in one specimen. VI. The hlastomeres of the 

 shaded areas in one specimen were not divided from each other. 1, 2, 3, successive 

 planes of division, ar, anterior right quadrant, pr, posterior right quadrant. 

 ar', pr', etc. areas separated off by the third segmentation-furrow. (After WATASE.) 



1 WATASE, S., Jour, of Morph., rv. 1891, p. 247, Plates. 



