MORPHOCHORETIC PATTERN 



FERTILIZATION 



323 



d.p.l. 



Fig. 14. Modification of the internal structure of a frog egg after fertilization, (a) The egg 

 was oriented animal pole up, fertilized by a tiny drop of sperm suspension between the ani- 

 mal pole and equator, fixed i h. later and cut along its axis and in the plane of the pigmented 

 spermatic track (d). The spermatic aster has developed and the two pronuclei have joined 

 in its central area. The vegetal cupule formed of big platelets and due to primary vitel- 

 logenesis {cf. p. 314 and Fig. 4-7) begins to disaggregate both near the spermatic track and 

 opposite to it. The inferior limit of the pigment, primarily horizontal, has begun to move, the 

 side opposite to the sperm-entrance point elevating (d.p.l.), the other, lowering (v.p.l). (b) 

 Egg treated the same way but fixed 2 1/2 h. after localized fertilization. The spermatic 

 aster has faded, the spermatic track leads to the fused pronuclei, the yolk cupule has modi- 

 fied even more, especially in the part farthest from the sperm entrance point, and the yolk 

 wall (y.w.) has been formed there. Its presence under a shallow layer of cytoplasm and some 

 remnants of melanic pigment result in the aspect of the grey crescent (gr. cr) . From now 

 on the dorsal side (d) and the ventral side (v.) are fixed, if the polarity is not experimentally 

 modified (see p. 343). From Ancel and Vintemberger, 1948. 



Fig. 15. Schematic representation of the changes occurring in a frog egg submitted to a 

 symmetrizing rotation, (a) The egg in its initial position (Fig. 30, a) with its pigment (dots) 

 and yolk cupule (dashes) quite symmetrical relative to the polar axis. The animal pole 

 (a.p.) bears the maturation depression; the vegetative pole (v.p.) has a small pigmented dot 

 serving as a landmark, (b) The gravitational rotation of the egg inside its somewhat viscous 

 perivitelline fluid has first brought the polar axis to a vertical position (interrupted line i) 

 but the gliding of the cortex, shown by the pigment, has transferred the maturation de- 

 pression toward the side opposite the direction of the rotation (broken line 2). This side will 

 be ventral and the yolk wall and grey crescent will appear opposite (under D). From Ancel 



and Vintemberger, 1948. 



Literature p. 483 



