290 THK PHYSIOLOGY OF REPRODUCTION 



membrane has l>een found to consist of pure iiiucin. 1 In Teleostean 

 fishes it lias IKH-II investigated in the case of the perch, 2 and found 

 t.. U> of the nature of a inucin. 



It would 1* interesting to find out by systematic investigations, 

 such as those of Pregl 3 and Buchtala, 4 whether the chemical nature 

 of the substances protecting the egg varies with the different 

 xoological classes, or whether there is a chemical adaptation to 

 external environment. 



The investigations of Hammarsten brought to light the interesting 

 fact that a chemical change takes place in the cover of the eggs 

 during ri]>ening. The immature eggs swell with water, and a 

 mucilaginous solution of mucus is formed, from which the mucin 

 may lx> precipitated by the addition of acetic acid. ' If mature eggs 

 are treated with water they do not swell. The water dissolves out 

 the contents of the egg and the empty covers of the eggs remain, 

 and can l>e transformed into mucin by weak alkali. During the 

 ripening of the eggs there is therefore a change from mucin to 

 mucinogen. 



The composition of the eggs of fishes is essentially the same as 

 that of birds' eggs. From the eggs of salted herrings Hugounenq lias 

 obtained the following figures calculated in percentage of the dried 

 material : - 



Per Cent. 



Pure fats - 10'35 



Phosphorised fats 6'53 



K.T.itin 2-27 



Protein ("clupeovin") - 81'47 



The organic constituents consist chiefly of protein, fats, and 

 phospborised t'ats, with some cholesterin. 



The following analysis of the ash of caviar-"' gives an idea of the 

 coiuiosition of the ash of the eggs of fishes: _ 



Total ash - K 2 O. Na.,0. CaO. Fe. 2 O ;! . P 2 O 5 - Cl. 



770 per cent. 3 -33 3077 5'02 0-22 lO'oo 47 -44 



Iii the egg the protein is present in the form of a phosphoprotein. 

 Valenciennes and Fn'my, who were the first to isolate this substance, 

 called it Ichtlmlin. Liter Walther showed that this substance very 

 closely resembles the vitellin present in birds' eggs. On peptic 

 digestion it yields an ii -on-containing pseudonuclein. A similar 



-i. ' Ktud.-s sur la Composition chimique de 1'CEuf et de ses 

 reloen , | 1( . x . laQrenooille commune," ZeiUd,. f.physiol. Chem., vol. vii., 1883 

 manten, 'Th-mie dea Fischeies," M,,,,V/ W . \\rch.f. Physiol., vol. xvii, 



i;i*r die Eihaute von ,W//,,,,, .<(,!/, ,,-e und ihre Abbaunrodukte, 

 tvh. j. pkaM. '7,.,,,^ v ,,i i vi 1908 



4 Bii. l.tala, /W. V 



:> Albu and Neu)*rg, J/iMi/*tf>/irer/itel t p. 241. 



