BIOCHEMISTRY OF THE SEXUAL ORGANS 277 



has as yet not been proved with certainty, although the 

 diastatic action of egg yolk observed by Mliller 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 eitherof 

 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 jiAatus and Crocodilus biporcattcs, and in 

 Elasmobranchs, Uke Raja and Scyllium, the membrane is stated 

 to consist of a keratin ? In the membrane of the eggs of Tropi- 

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

 which is free from sulphur and resembles the elastin which 

 constitutes the elastic fibres of mammahan connective tissue. 

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

 Mustelus IcBvis.^ But these data are very scanty and hardly 

 convincing. In Amphibians Uke 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 found 

 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 diastatisohes Ferment im Hiihnerei," 

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



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

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

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



' Hilger, " Ueber die Chemischen Bestandteile des Reptilieneis " ; Berichte 

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



* Krukenberg, toe. cit., 2 Abteilung, 1882. 



° Giaoosa, " Etudes sur la Composition chimique de I'CEuf et de ses En- 

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



' Hammarsten, "Chemie des Fischeies," Skandinav. Arch. f. Phyaiologie, 

 vol. xvii., 1905. 



' Pregl, ' ' tJber die Eihaute von Scyllium stellare und ihre Abbauprodukte," 

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



' Buchtala, ibid. 



