370 



NOTE ON THE PIGMENTATION OF EROGS' EGGS. 



By Latjncklot Harrison, B.Sc. (Syd.) B.A. (Cantab.), Afting-Professor of 

 Zoology in the University of Sydney. 



On page 4 of the second volume of the new Text-book of Embryology 

 ("\^ol. ii., Vertebi-ata, Macmillan, Londun. 191!)) Professor Graham Kerr makes 

 some obsei"vations upon the jjigmentatiou of the egg in Ganoids and Amphibians. 

 These remarks would appear to be based upon the experience of a limited group 

 of workers with a small number of frog species. While nothing is stated dog- 

 matically by Professor Kerr, his remarks liave the appearance of a general 

 statement, yet they are not in accord with my own observations upon the eggs 

 of Australian Anura. It has appeared to me, therefore, worth while to place 

 on record the discrepancies I notice, particularly a.s the Text-book will be 

 used largely by students whose |">owers of diseriminatiim liavc not been deve- 

 loped, and who are aj)t to consider as conclusive any statement tliat they read 

 in such a work. 



Professor Kerr writes : — "Many eggs on the other hand especially amongst 

 tlic Ganoid fishes and the Amphibians are priven a dark colour by the presence 

 within them of brownish-black pigments belonging to the melanin group. Such 

 jiignient appears to be of definite l)iological significance, jiroviding as it does 

 an opaqiu' coat wliich |)rotects the living protoplasm from tlie harmful influence 

 of light.' Eggs in which it occurs develo)), :us a rule, under conditions where 

 they arc exposed to intense daylight. The eggs of ordinary Frogs and Toads 

 for esaniple which are surrounded by clear transparent .ielly have a well 

 developed pigment coat. On the other hand in the case of Frogs and Toads 

 whose eggs are suiTounded t)y light-proof foam or are deposited in burrows 

 underground they are commonly without pigment. 



"In all ]>robability this dejiosition of melanin jiiginent in the superficial 

 ))rotoplasni of tlic egs;- (normally in its upper portion) is to be interpreted as 

 having been orif.'-inally a direct reaction to the influence of liglit. tlie metabolism 

 being so affected as Id bring about the fonnation of this i);irticiihir iron-con- 

 taining exci'ctory pigment. 



"It may be ol)jected that the pigment is produced before the egg is laid 

 (e.g. the Common Frog) and therefore before it is exposed to the action of 

 light, but a-s a matter of fact the body-wall of the adult is by no means 

 opaque to light rays and even while still in the ovary the egg's are ex|iosed to 

 the influence of faint liglit. If we may t:d<e it, as seems' probable, that the 



