264 LILLIE. [Vol. XVII. 



the course of subsequent events guided by their unbroken 

 continuance. 



These forces are responsible in part for the paths of the 

 germ-nuclei, the elongation of the sphere substance, the defi- 

 nite position and shifting of the spindle, and later, to a great 

 extent, for the equality or inequality, the rate, and the direction 

 of the early cleavages. 



The observations and experiments that force on us the con- 

 clusion that the cytoplasm of the ^'gg is definitely organized 

 are now so numerous that a book would be required for their 

 adequate consideration, I will therefore refer to only a few 

 typical examples. Watase ('90) shows that the unsegmented 

 blastoderm of the squid {Loligo) is bilateral in structure, the 

 nucleus being situated excentrically nearer the end of the 

 blastoderm that is to become the posterior end of the embryo. 

 The blastoderm is at the pointed end of the nearly oval Q.gg, 

 which is more convex on the surface corresponding to the 

 anterior end of the blastoderm. Watase does not hesitate to 

 attribute the bilaterality of the blastoderm to the distribution 

 of different protoplasmic substances. He cites the following 

 interesting extract from van Beneden and Neyt on Ascaris 

 (1887) : " Les premiers blastomeres ont, comme I'oeuf feconde, 

 non seulement une symetrie monoaxone, mais une structure 

 bilaterale. II est probable que c'est la un caractere commun a 

 toute cellule et Ton doit concevoir un organisme cellulaire, non 

 comme forme de couches concentriques, mais comme presen- 

 tant essentiellement un axe a extremites differents et un plan 

 unique de symetrie. Cette symetrie bilaterale de la cellule 

 est probablement la cause de la symetrie bilaterale des orga- 

 nismes plus complexes, des animaux en particulier." 



McMurrich's observations ('95a, '95b) furnish interesting evi- 

 dence of a high grade of organization of the ova of Isopoda. 

 Injaera the segmented e.gg is a syncitium, the cells being 

 really local nucleated accumulations of a continuous cytoplasm 

 in which the yolk is imbedded. The Qgg is oval, so that it is 

 possible to recognize an anterior (broader) and posterior (nar- 

 rower) end. In the 8-celled stage the arrangement of the cells is 

 as follows : four cells at about equal distances apart surrounding 



