I30 PATTERNS AND PROBLEMS OF DEVELOPMENT 



OOCYTE AND UNDIVIDED EGG 



Differential dye reduction in early, growing oocytes of echinoids"^ seems 

 to indicate a very slight decrease in rate of reduction from the region where 

 the nucleus is nearest the cell surface. This is usually, but by no means al- 

 ways, nearer the free than the attached pole. In full-grown oocytes ap- 

 proaching maturation, with nucleus no longer visible and retaining evi- 

 dence of position of stalk of attachment, a slight reduction gradient with 

 highest rate at the pole opposite the region of attachment seems to be 

 present: maturation stages have not been obtained. In a few unfertihzed 

 eggs after maturation a slight gradient, with most rapid reduction at the 

 egg surface in the region opposite the pole of attachment, or in some eggs 

 in the region where the nucleus is near the surface, has been observed; but 

 whether the nucleus is still at the apical pole or elsewhere is not known. 

 In all stages preceding fertilization these reduction gradients are so slight 

 that their presence becomes reasonably certain only with repeated ob- 

 servations. Only uncertain indications of a possible differential suscepti- 

 biUty have been observed in echinoid stages preceding fertilization (Child, 

 1916a). A higher susceptibility to cyanide of the ventral side in the undi- 

 vided egg of the sea urchin Paracentrotus lividus has been reported (Foer- 

 ster and Orstrom, 1933). 



The nucleus of the full-grown asteroid oocyte usually lies near the cell 

 surface at some point, more often nearer the free than the attached pole. 

 With slight staining, reduction apparently decreases in rate from that 

 part of the cortical region where the nucleus is nearest the surface; but 

 here, as in the echinoids, the gradient is at best very sUght. According to 



the terms "apical" and "basal" are often used in place of them, as being more convenient. 

 Gradients observed are often designated as "basipetal" or "acropetal," meaning that the 

 progress of the change indicating the gradient is basipetal, toward the vegetal or basal pole, or 

 acropetal, toward the animal or apical pole. In echinoids the apical polar region becomes the 

 oral lobe of the pluteus larva (see Fig. 73), the basal region, mesenchyme, and entoderm; and 

 the most basal region of the ectoderm becomes the anal side of the pluteus. The apical polar 

 region of the asteroid starfish egg becomes the apical and functionally anterior end of the 

 larva (see Fig. 83). The so-called "ventrodorsal axis" of the echinoid and asteroid larva is 

 more or less nearly at right angles to the apicobasal or polar axis; that is, one side of the em- 

 bryo becomes conventionally ventral, the opposite side dorsal. The ventral side of the echinoid 

 pluteus, the side including the oral lobe and the anal arms (see Fig. 73), is functionally anterior 

 and has sometimes been called "anterior" (Child, 1915a, 1916a, d), sometimes the "oral side" 

 or "field"; the opposite pointed or rounded end of the pluteus, "posterior" or "aboral." In the 

 asteroid larva, however, the ventral side is oral, and the anus comes to lie more or less ven- 

 trally. 



^f- Material, Strongylocentrolus purpuraliis, Deudraster excentricus; dyes, methylene blue and 

 Janus green; Child, 1936a. In this paper dye concentrations and staining periods are given 

 for all figures. 



