BY LAUXCELOT HARRISON'. 371 



influence of natural selection has gradually developed in sueh cases the particular 

 type of sensitiveness to light which leads to tlie foiination of melanin, on ac- 

 count of its protective value, then there is nothing surprising in the developing 

 of this sensitiveness at earlier and earlier periods until at last it has resulted 

 in the pigmentation of the stUl intra-ovarian egg in response to the feeble light 

 raj's which penetrate the body wall." 



There can be no disagreement with a statement that the eggs of most 

 Anura have a pigmented upper pole. This may vary in size from a small polar 

 cap {Pseudoplirtfiie} to considerably more than a hemisphere (Eana temporaria) ; 

 and in colour from light brown (llijhi ewivgii) to intense black (Crinia signi- 

 fera). But several instances have been given of Anviran eggs whicli are with- 

 out pigment. 



Thus Agar (1009, p. 89.5) writes of Ph yllomedusa sauvagii — "The eggs are 

 quite uupigmeuted, and any that are exposed to the surface, as happens often 

 in less perfectly formed nests, turn yeUow and die." Budgett (1899, p. 315) 

 mentions the spawn of Phiillomedusa Iii/pochondrialis as — "batches of white 

 eggs in masses of firm jelly.'' Agars Figure 2 shows cjuite plainly that the 

 intra-ovarian eggs are without pigment. In the case of PhyUomedusa, then, 

 we have undoubted white eggs, presumably as the eggs are enclosed in light- 

 proof foam. But Pliiillomedusa is a small, comparatively translucent frog, 

 which lies by day on the upper surfaces of leaves, fully exposed to light (Budgett, 

 1899, p. 314) ; so that if pigment be a direct reaction to light, one would expect 

 to find in this case the eggs definitely pigmented. 



In three species of Limnod;/nastes with the breeding habits of which I am 

 familiar, the eggs are also laid in a mass of foam, which from its nature must 

 reflect and refract so much incident light as to be practically light-proof. Tet 

 the eggs are densely pigTiiented, as are the developing larvae. L. dorsalis is a 

 burrowing frog, never seen by daylight at ordinary times, and resorting to 

 water only for a day or two in the breeding season. L. peronii is a cniitozoic 

 form, found under stones, etc., by day, and resorting to water at night. This 

 species may, however, be found in the water during the daytime within the 

 limits of its spawning season. L. tasmam'e'nsi.s is also cryptozoic, and I have 

 only once found it in water by daylight. Ni ue of these species would appear 

 to be susceptible to the influence of daylight acting througli their robust body- 

 wall, yet the intra-ovarian eggs are densely i)igmente<l. It may be noted in 

 passing tliat eggs entangled in the upper jiortion of the foam die, not from ex- 

 posure to light, but because of insufficient moisture in this region. 



There is thus a very marked ilifference between Plnilldmednsa and Limnody- 

 ncistee, and if would seem that the explanation of pigmentation is further to 

 seek than Graham Kerr's general statement would have us believe. 



Besides Phyllomedusa, certain other frogs have been reported as laying 

 eggs without pigment. Of Paludicola ftixomaculata Budgett wi'ites (1899, p. 

 309) — "The eggs . . . are found embedded in a frofliy mass floating upon the sur- 

 face of the water and are without pigment.'" Bles (1907, p. 445) 



dealing witli Budgett's material of this species writes — "The o\Tim is quite free 

 from pigment. In the earliest stage examined, the blastopore is veiy small." 

 In view of what I have to say below, the latter sentence may bear some 

 significance. Otherwise Paludicola spawn would appear to resemble that of 

 Limnndyiiastes, except for the absence of pigment. 



Budgett (1899, p. 311) records the nests of Engystoma ovale as — "holes in 

 the ground beneath fallen tree trunks, of the size of a cricket ball and lined with 

 a froth containing white eggs, and also tailed larvae." 



