of the Fishery Board for Scotland. 



137 



lecithin, although those who held this opinion might have seen how 

 erroneous it was if they had read Valenciennes and Fremy's paper, where 

 it is stated that the percentage of phosphorus remained high (3 per cent.) 

 even after prolonged extraction with warm alcohol and ether. Lecithin is 

 always found with it, but can be removed in the way above described. 

 Miescher found these plates in tlie eggs of Bombinator, and showed that 

 in every hundred parts of the yolk-plates, sixteen were composed of 

 lecithin. Miescher noticed also that the ash, after incineration, of this 

 substance reacted acid, that is to say, phosphorus had been present in 

 organic combination, not bound to bases. He also was the first to show 

 that, after gastric digestion of the plates, an insoluble residue, containing 

 phosphorus, was left ; and, from his examination, he thought he was 

 dealing with a nuclein similar to that present in the nuclei of pus cells. 

 It differs from these true nucleins in, as I have said before, not furnish- 

 ing nuclein bases. The other constituents present in the yolk are fat, 

 lecithin, albumin, inorganic salts, organic salts, cholesterin, pigments, 

 and water. 



Nucleus. 



The nucleus, or in the case of the ovum, the germinal vesicle 

 contains different albuminous substances, which are mostly characterised 

 only by their affinity for certain stains. The chromatin of the histologist 

 has been supposed to be identical with the nuclein of the physiological 

 chemist, and has always been referred to as the important constituent of 

 the nucleus. It is a phosphorus-holding albuminous substance, which is 

 very resistant towards action of pepsin. It is characterised by the fact 

 that on decomposition it furnishes nuclein bases. It is composed of an 

 organic acid which contains all the phosphorus of the nuclein — nucleic 

 acid — bound to more or less albumin. In the condition of mitosis, the 

 organic phosphorus-holding acid, nucleic acid, is supposed to exist in 

 the free state ; but all our evidence in support of this is based simply on 

 staining affinities of the acid, and is not conclusive. 



I do not believe that this true nuclein is present in the germinal 

 vesicle of all resting ova, except in very small quantity. In fact, even 

 when I have used large quantities of immature ova, I have been able 

 to obtain it only in small amount. But when the ovum is fertilised 

 true nucleins soon appear. Whether formed from albumen, or added 

 on by the male pronucleus, I do not know. The subject still requires 

 investigation. The paranuclein or pyrenin of the histologists is not 

 definitely characterised, either histologically or chemically. Linin 

 (Schwarz) is also an exceedingly indefinite body, as also Zaccharias' 

 amphipyrenin, the substance present in the nuclear membrane. 



Vitelline Membrane. 



The vitelline membrane is of a proteid nature, and is secreted by 

 the ovum itself. 



Reaction of Yolk. 



All specimens of yolk which I have examined react acid when fresh, 

 but if one incinerate the fluid, the ash which is obtained reacts alkaline ; 

 that is to say, the acidity is due to an organic acid, probably lactic acid. 



The description of the changes which take place during maturation 

 of the ovum with regard to the entrance of substances from without, and 

 their passage to different parts of the ovum, I shall give later, when I 

 have run over shortly the changes in specific gravity, etc., of the ova as 

 ripening proceeds. 



