PROMORPIWLOGICAL RELATIOXS OF CLEAVAGE 



3S 



the narrow end, according to Watase, representing the dorsal aspect 

 the broad end the ventral aspect, the flattened side the posterior 

 region, and the more convex side the anterior region. A// the early 

 cleavage-furroivs are bilaterally arranged ivith respect to the plane of 



a 



-1^ 



Fig. i8o. — Eggs of the insect Corixa. [Metschnikoff.] 

 A. Early stage before formation of the embryo, from one side. />'. The same viewed in the 

 plane of symmetry. C. The embryo in its final position. 



a. anterior end; p. posterior; /. left side, r. right; f. ventral, d. dorsal aspect. (These letters 

 refer to theyf«a/ position of the embryo, which is nearly diametrically opposite to that in which it 

 first develops) ; m. micropyle ; near/ is the pedicle by which the egg is attached. 



symmetry in the nndivided egg ; and the same is true of the later 

 development of all the bilateral parts. 



Scarcely less striking is the case of the insect ^^^. as has been 

 pointed out especially by Hallez, Blochmann, and Wheeler (F'igs. 

 62, 180). In a large number of cases the ^^g is elongated and 



