BIOCHEMISTRY OF THE SEXUAL ORGANS 289 



egg abcmt O'l per cent. During the first twelve days of incubation 

 it increases to about five times the initial value and then, after a 

 slight fall, remains stationary during the rest of development. 

 Guanidin is probably split off from arginine, which contains the 

 guanidin group in combination with an amino acid. 



With regard to the question of the presence of ferments and their 

 significance we are on very difficult ground. We must here clearly 

 distinguish between endo-enzymes and secreted enzymes. The 

 endo-enzymes comprise all those enzymes which are so closely bound 

 up with the protoplasm that they can be isolated only after the cell 

 has been destroyed. Their sphere of activity is therefore limited to 

 the inside of the cell. Such endo-enzymes are present in every organ, 

 and have also been found in the egg, 1 producing proteolysis and 

 lipolysis. But since such endo-enzymes are present in many, if not 

 in all cells, no special significance can be attached to their presence 

 in the eggs. 



The presence in the egg of secreted ferments analogous to the 

 ferments which can be obtained by simple extraction from the 

 digestive glands of the adult animal, would allow of more definite 

 conclusions. The presence of such ferments has as yet not been 

 proved with certainty, although the diastatic action of egg-yolk 

 observed by Miiller and Masuyama' 2 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 jnbatus and Crocodilits biporcatiis, and in Elasmobranchs, 

 like Raja and Scyllium, the membrane is stated to consist of a 

 keratin. 3 In the membrane of the eggs of Tropidonotus* 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 Mmtclux Iw-vix? But these data are very 

 scanty and hardly convincing. In Amphibians like the frog the 



1 Wohlgemuth, " Uber das Vorkommen von Fermenten im Hiihnerei," 

 Fettoekrifi fto Salkowtki, 1904. 



2 Miiller and Masuyama, "tiber ein diastatisehes Ferment im Hiihnerei," 



ZeitxcLf. AW., vol. xxxix., 1900. 



3 Krukenberg, Vcryleichende Phi/sioloyische Sttuttg*, II. lleihe, 1 Abteiluiif, 

 1882. Neumeister, " Uber die Eischalenhiiute von Kc/tidna und der Wirbeltieiv 

 im allgemeinen," Zeitsch. f. fiiol., vol. xiii., 1895. 



4 Hilger, " Ueber die Chemischen Bestandteile des Reptilieneies," l}i-ri<-htc 

 ill- 1- ili'iitm'ltc.ii ,'ficin. (iesellschaft. vol. vi., 1873. 



5 Krukenberg, lo<: cit., 2 Abteilung, 1882. 



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