PHYSIOLOGICAL CHARACTERISTICS OF AXIATE PATTERNS 157 



is, oxygen was completely excluded from the beginning. The lesser differ- 

 ences in rate are undoubtedly more clearly distinguishable with gradual 

 oxygen decrease than with complete exclusion at once. Probably with 

 gradual decrease of oxygen a reduction gradient progressing basipetally 

 from the apical pole would have appeared instead of reduction of the 

 apical hemisphere without differential. 



In eggs and embryos of Triturus rividaris there is considerable variation 

 in depth of pigmentation. Some lots of eggs were found by Child to be 

 light enough to permit observation of reduction. -^^ With gradual decrease 

 of oxygen dye reduction could be observed to progress basipetally in 

 blastulae, but whether a dorsiventral differential was present could not 

 be determined; if present, it was very slight. In the naked early gastrula, 

 however, reduction was most rapid at the dorsal border of the blastopore 

 and progressed laterally and anteriorly from this region. Apical and dorsal 

 reduction could not be observed in the same individual because of the 

 flattening, but embryos in proper orientation showed reduction decreasing 

 in rate from the apical region basipetally. In stages with open neural 

 plate rate of reduction appears highest in the floor of the plate and de- 

 creases from the anterior region posteriorly. It occurs over the whole 

 plate, including a narrow region just outside the neural folds, before re- 

 duction is clearly evident in the general ectoderm." A few observations 

 on elongated embryos with closed neural folds showed rate of reduction 

 decreasing from the head posteriorly along the dorsal region and laterally 

 and ventrally from that, with a posterior region of higher rate as develop- 

 ment of the tail began. 



Using the method of Giroud and Bulliard (1933) for indicating occur- 

 rence and distribution of sulphydryl compounds by a color reaction, 

 J. Brachet (1938) has shown a definite and changing distribution during 

 development of several amphibians of what he believes to be sulphydryl- 

 proteins. In the unfertilized egg and soon after fertilization the reaction 

 occurs in a region about the apical pole. Some 2 hours later it is localized 

 more or less closely in a crescent, corresponding, in forms in which dorsal 

 and ventral sides are distinguishable, to the position of the gray crescent 

 of the frog's egg. In later cleavage and blastula stages the reaction occurs 



^^ Slight staining with Janus green of blastulae within the membrane was found possible 

 after removal of the jelly. With care the membrane can be removed from gastrulae; but, when 

 naked, the gastrulae become flattened on the surface in contact. 



37 The Triturus material was provided through the kindness of Dr. V. C. Twitty, and his 

 skill in removing the membranes of early gastrulae was of great assistance. 



