DEMONSTRATION OF AXIAL GRADIENTS. 14! 



of fact, penetration of the perisarc apparently occurs almost at 

 once, and the differences in rate and depth of staining at different 

 levels appear to be very much greater than the differences in 

 perisarcal penetration. 



The developmental stages of the egg of the hydromedusa, 

 Phialidium from the ovarian egg to the hydroid have been ex- 

 amined with permanganate. In the ovarian egg, isolated by 

 teasing, the region of the egg next to the free surface of the gonad 

 stains most rapidly, with a color gradient from this region to the 

 basal egg-pole. This gradient persists during fertilization, 

 cleavage and to the advanced planula stage, the region of most 

 rapid staining being the apical end of the embryo. In the late, 

 elongated planula, just before attachment, a second region of 

 rapid staining arises at what was originally the basal end, the 

 planula attaches itself by its apical end, and the first hydroid 

 arises as a bud from this second region of rapid staining at the 

 basal end. The fact of attachment of the planula by the apical 

 end and the development of the first hydranth from the original 

 basal end has long been known to embryologists, and the MnO 2 

 color gradients merely serve to give some indication of the 

 physiological conditions concerned. Apparently the first hy- 

 dranth is physiologically a bud, a process of agamic reproduction 

 in the planula, resulting from physiological isolation at the basal 

 end, a process similar to the development of a second hydranth 

 at the tip of the stolon in Tubularia (Child, '156, pp. 91-92) 

 the development of segments in annelids (Hyman, '16 Child, 

 '17^), and many other reproductive processes in other forms 

 (Child, '156, Chapter V.). These results on hydrozoa are in 

 agreement with those obtained by other methods, except that 

 as regards unfertilized eggs, cleavage stages and general colony, 

 gradients, the permanganate results are more distinct and 

 definite. 



The color gradients have been determined in one species of 

 siphonophore belonging to the family Monophyidse, a form with 

 a single, elongated nectocalyx, from one side of which the stem 

 or ccenosome bearing the groups of zooids arises. The necto- 

 calyx, which is of course a modified medusa, is morphologically 

 bilaterally symmetrical and shows in permanganate, not only a 



