BIOCHEMISTRY OF THE SEXUAL ORGANS 277 



has as yet not been proved with certainty, although the 

 diastatic action of egg yolk obierved by Mtiller and Masuyama * 

 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, Uke Calotes jubatus and Crocodilus biporcatus, and in 

 Elasmobranchs, like Raja and Scyllium, the membrane is stated 

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

 donotics,^ 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 

 Mmtelus Icevis} But these data are very scanty and hardly 

 convincing. In Amphibians hke the frog the membrane has 

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

 it has been investigated in the case of the perch,* and foimd 

 to be of the nature of a mucin. 



It would be interesting to find out by systematic 

 investigations, such as those of Pregl ' and Buchtala,^ 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. 



' Miiller and Masuyama, " ijber ein diastatisches Ferment im Hiihnerei," 

 Zeitschr.f. Biologie, vol. xxxix., 1900. 



^ Krukenberg, Vergleichende Physiologische Studien : II. Reihe, 1 Abtei- 

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

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



^ Hilger, " Ueber die Chemisohen Bestandteile des Reptilieneis " ; Berichte 

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



* Krukenberg, loc. cit., 2 Abteiiang, 1882. 



^ Giaoosa, " Etudes sur la Composition chimique de I'OSuf et de ses En- 

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



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

 vol. xvii., 1905. 



' Pregl, " tjber die Eihaute von Scyllium stcllare und ihre Abbauprodukte," 

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

 ' Buohtala, ibid. 



