478 J. BRONTE OATENBY 



are undescribed in the text. In some cases it is impossible to 

 know whether Hemon's figures of supposed nuclei are cells or 

 nucleoli ; this applies especially to his Tafel IX, figuring 

 early stages of development. 



Writing of the full-grown egg, Seraon says : ' Die Keimscheibe 

 ruht auf einem Lager von feinkornigem, weissem Dotter, und 

 dieser entsendet nach innen eine strangformige Fortsetzung, 

 einen " Dotterstiel ", der im Centrum sich flaschenformig zu 

 einer Latebra aufblaht. Die Elemente des gelben Dotters 

 sind kugelrund ; gegen den weissen Dotter zu, besonders in der 

 Gegend der Keimscheibe, nimmt der Durchmesser der Kugeln 

 des gelben Dotters continuirlich ab. An der Grenze erblickt 

 man haufig die Kugeln des gelben Dotters in alien Stadien des 

 Zerfalls zu kleineren und kleinsten Elementen. In gleichem 

 Maasse wie das Blastoderm den Dotter umwachst, breitet sich 

 an der Oberfiache des letzteren und ersteren eine Schicht von 

 weissem Dotter aus.' 



In his figures of sections of the eggs of both Echidna and 

 Ornithorhynchus, Semon draws, within the more central part 

 of the cross-section of the egg, from one to as many as three 

 concentric rings lying in the yellow yolk, as is well known to 

 occur in the hen's egg, but. he does not describe these rings in 

 his text. His description of the structure of the egg is very 

 poor. It would probably be worth while for a capable cytologist 

 to re-describe the sections of eggs of both Echidna and Ornitho- 

 rhynchus procured by Semon's party in Australia. 



3. General Note on the Structure of the Egg of 



THE SaUROPSIDA, 



In both the Aves and the Reptilia, the egg, as is well known, 

 has a very complicated structure, and for the purpose of 

 comparison with that of Ornithorhynchus I have given a 

 diagram in Text-fig. 1. 



The germinal disk (gd) is formed of pure protoplasm free of 

 any but the smallest yolk-spheres ; this protoplasmic disk 

 contains a very granular, generally somewhat basophil, type 

 of protoplasm, which can readily be distinguished from the 



