has as yet not been proved with certainty, although the 

 diastatic action of egg yolk observed by Miiller and Masuyama l 

 points to the presence of a diastase analogous to the ptyalin 

 of the saliva. 



Lower Vertebrates 



The covering of the eggs of the lower Vertebrates is either of 

 the nature of a keratin, a scleroprotein rich in sulphur, similar to 

 the membrane of birds' eggs, or it is a mucoid substance. In 

 reptiles, like Calotes jubatus and Crocodilus biporcatus, and in 

 Elasmobranchs, like Raja and Scyllium, the membrane is stated 

 to consist of a keratin. 2 In the membrane of the eggs of Tropi- 

 donotus, 3 the British grass snake, a substance has been found 

 which is free from sulphur and resembles the elastin which 

 constitutes the elastic fibres of mammalian connective tissue. 

 A similar substance is stated to occur in the egg-membrane of 

 Mustelus Icevis.* But these data are very scanty and hardly 

 convincing. In Amphibians like the frog the membrane has 

 been found to consist of pure mucin. 5 In Teleostean fishes 

 it has been investigated in the case of the perch, 6 and found 

 to be of the nature of a mucin. 



It would be interesting to find out by systematic 

 investigations, such as those of Pregl 7 and Buchtala, 8 whether 

 the chemical nature of the substances protecting the egg varies 

 with the different zoological classes, or whether it is dependent 

 upon external circumstances representing perhaps a case of 

 chemical adaptation. 



1 Miiller and Masuyama, " liber ein diastatiscb.es Ferment im Hiihnerei," 

 Zeitschr. f. Biologic, vol. xxxix., 1900. 



2 Krukenberg, Vergleichende Physiologiache Sttutien : II. Reihe, 1 Abtei- 

 lung, 1882. Neumeister, " liber die Eischalenhaute von Echidna und der 

 Wirbeltiere im allgemeinen," Zeitschr. f. Biologic, vol. xiii., 1895. 



3 Hilger, " Ueber die Chemischen Bestandteile des Reptilieneis " ; Bcrichte 

 der deutschen chcm. Gesellschaft, vol. vi., 1873. 



4 Krukenberg, loc. cit., 2 Abteilung, 1882. 



5 Giacosa, " Etudes sur la Composition chimique de 1'OEuf et de ses En- 

 veloppes chez la Grenouille commune," Zeitschr. f. phys. Chemie, vol. vii., 1883. 



6 Hammarsten, " Chemie des Fischeies," Skandinav. Arch. f. Physiologic, 

 vol. xvii., 1905. 



7 Pregl, " Uber die Eihaute von Scyllium stellare und ibre Abbauprodukte," 

 Zeitschr. f. phys. Chemie, vol. Ivi., 1908. 



8 Buchtala, ibid. 



