PHYSIOLOGICAL CHARACTERISTICS OF AXIATE PATTERNS 131 



E. B. Wilson and Mathews (1895), that region of the oocyte where the 

 nucleus is nearest the surface becomes the apical or animal pole in Asterias 

 forbesii, and the polar bodies form there. Polar bodies in this species are 

 said by Yatsu (1910a) always to appear halfway between equator and 

 free pole. In Patiria miniata, another asteroid genus, their position, like 

 the position of the oocyte nucleus, is highly variable, ranging fron the free 

 pole to a position between equator and attached pole (Child, 1936a, Figs. 

 12-14). According to Schaxel (1914; 1915, pp- 35, 36) the attached pole 

 becomes the apical pole in Asterias glacialis; this is not the usual relation 

 of egg polarity to ovarian attachment in echinoderms or other inverte- 

 brates. 



When maturation of the Patiria egg begins, a very distinct cortical dye- 

 reduction gradient appears, with most rapid reduction in the region of 

 polar-body formation (Fig. 43, A). When the cell is stained throughout, 

 reduction progresses basipetally in the interior as well as in the cortex 

 (Fig. 43, B). The region about the vegetal pole reduces last, but little or 

 no gradient is visible there. The susceptibility gradient with cyanide in 

 the ovarian oocyte oi A. forbesii (Fig. 43, C, D) progresses from the region 

 where the nucleus is nearest the surface through the whole cell (Child, 

 1915a). The oocyte nucleus, whether in the cell or isolated, also shows a 

 susceptibility gradient the same as that of the cytoplasm in nuclei not 

 isolated (Fig. 43, £). Whether this actually represents a nuclear gradient 

 or results from differential exposure of the nucleus as cytoplasmic cytol- 

 ysis occurs is not certain, but the differential susceptibility of isolated 

 nuclei suggests a real nuclear gradient. Conceivably a nuclear gradient 

 might be determined by the differential of its position near the surface of 

 the cell. 



From experiments with hypertonic and hypotonic solutions Dalcq 

 (1925) infers presence of a gradient of electrical charge on the plasma 

 membrane of the egg of A. glacialis with basipetal increase of positivity. 

 Under natural conditions the egg of A. forbesii does not show the migration 

 of alkaline and acid substances to opposite polar regions observed in some 

 other eggs, probably because of high viscosity of the cytoplasm, but under 

 conditions which decrease viscosity the bipolar migration occurs (Spek, 

 1934c). The migration is apparently in relation to the axis of attachment 

 of the egg in the ovary; but, if earlier investigators are correct, this is not 

 the final polarity of the egg and embryo. Spek's description and figures 

 indicate accumulation of acid substances at the pole of attachment, alka- 

 line substances at the free pole. 



