B 



A 



n 



Fig. 219, .4 -C— Cytoplasmic symmetry pattern of the ascidian egg, as postulated by 

 Dalcq. A, B, scheme of pattern derived from earlier investigations: "neurochordoplasm" 

 unshaded; "myochymoplasm" black; A, polar view with median plane and plane of first 

 cleavage indicated by broken line; B, lateral view with polar axis and approximately the plane 

 of second cleavage indicated by broken line (after Dalcq, U organisation de Vauf chez les 

 Chordes, 1935). C, organization of the unfertilized egg, according to Dalcq's experiments on 

 double merogony. An and Vg, animal and vegetal poles; H, side of the future head; T, side of 

 the future tail; the plain semicircular lines represent the postulated cortical field with its decre- 

 ment from //; the dotted spots represent the mantle of yellow pigment lying just under the 

 cortex; the horizontal, interrupted lines represent the internal (yolk?) gradient with its 

 decrement from Vg (from a drawing provided by Professor Dalcq). 



