372 XOTE ox THE PIGMEXTATIOX OF FRO(iS' EG<!S, 



Bles (1907, p. 451), (leseribins;: Bii<lgett"s Gambiu material of Hemisus 

 marmoratum, writes: — "The earliest stages which wei-e preserved ai'e late seg- 

 mentation stages of which there is nothing special to note except that the eggs 

 are quite without pigment.'' 



Finally Dakin (1920, p. 242) describes tlie egg's of Ileleioporus ulbujjuuc- 

 iatus as "soniewhat lai-ge and without pigment." These eggs were laid at the 

 bottom of burrows 18 indies deep, in friable sandy soil, and were enclosed in a 

 mass of frothy mucus. 



It would appear then on the face of it tliat unpigmented frog-'s eggs are 

 of comparatively common oecuiTenoe. But the condition that I find in tlie 

 eggs of Pseudophryne austraTia and P. bihronii causes me to suspect that many 

 eggs described as being without pigment may not really be so. In these species 

 the unsegmented egg has a black upper pole, occupying in section about one- 

 sixth of the circumference of the egg. During the early stages of segmentation 

 the micromeres are confined to this caji, which retains its l)laek colour. As 

 overgrowth pi'oceeds, however, the pigmented area extends, but loses its in- 

 tensity of colour, so that by the time the blastopore ha.s become circular the 

 whole pigmented area is of so pale a grey a.s to be distinguishable with difficulty 

 from the white yolk. In eggs which have been preserved the distinction is even 

 less marked. Pigment appears again during the formation and closure of the 

 neural groove, but the embryo, when folded off, is practically without pigment. 

 In this case unless the eggs were observed in the early segmentation 

 stages they might easily be described as without |)igment. As most of the eggs 

 described as unpigmented are of a similar heavily yolked type, I believe the 

 same thing may ha\e happened in some at least of these cases. Eggs of Ilelein- 

 porus kindly sent me by Professor Dakin have all passed beyond the stage of 

 early segmentation, and have an appearance precisely similar to that of 

 Pseudophrijne eggs. In Budgett's material mentioned above, of PalmlicoJa and 

 Hemiaus there are no early segmentation stages. The material of Enrjii^toma 

 would ajipear to have })een lost, as no mention of it occurs in Bles' report 

 (1907). 



From ai)pearances observed in two species of Pscudophriine, and in several 

 species of Hi/la, the amount of pigment present seems to bear a definite relation 

 to the protoplasmic mass of the egg. The addition of fuitlu'i' yolk to the bulk 

 of the egg in the course of evolution is not accompanied by a cimiitcnsating 

 addition of pigment. As overgrowth proceeds, the amount of pigment present 

 ap])ears to remain practically constant. In small yolked eggv which are densely 

 pigmented there is little or no diminution of intensity of colour during over- 

 growth. In large-yolked eggs, however, owing to tlie much greater area which 

 has to be covered by the pigment, tliere is a very definite liglitening in colour, 

 from tlie black to palest gi'ey in Pseiidophrijtie, from dark brown to light yellow- 

 ish brown in several sj^ecies of liyla, a.s overgrowth proceeds. 



This view is opposed to that of T. H. Morgan (1891, ]>. 7.58) who main- 

 tains that black cells do not overgrow light, but that new pigmented cells are 

 cut off from tlia ujiper comers of the yolk cells, and — "there is a continuous 

 formation of new luginent taking place at the perii)liei"y of the black area 

 within th(> new cells that are being fonued." PignuMit production is admittedly 

 a i)roduct of active metabolism, and one would expect to find i)iguieiit being 

 foniied in the i-egion of tlie germ ring, but, in tlie eggs I mention, this wouM 

 not appear to be snilicient to gi-eatly affect the colour of the egg surface. 



Finally, both species of Pseudnphri/ne are cryptozoic in habit hiding by day 

 under logs and heaps of refuse, and laying their eggs in similar situations. 



