ITS CHEMICO-PHYSICAL AND MORPHOLOGICAL PROPERTIES 51 



they are very numerous, they show considerable differences in their 

 size. Very frequently a few small vacuoles filled with fluid are to 

 be seen. The examination of living egg-cells shows that these 

 vacuoles are not artificially produced. Additional vacuoles may 

 be formed after the death of the egg, whilst those already present 

 may increase in size, as has been pointed out by Fleniming (II. 10, 

 p. 151). 



These germinal spots differ in their chemical properties from true 

 nucleoli, which consist of paranuclein and do not become stained 

 with the usual nuclear staining reagents. On the other hand, it 

 has not yet been discovered whether their substance is quite iden- 

 tical with the nuclein of the framework. Up to the present 

 this point has not yet been satisfactorily worked out, in spite 

 of the numerous experiments which have been made upon the 

 nucleus. One thing alone can be accepted as certain that the 

 more or less rounded bodies present in various plant and animal 

 nuclei, which in scientific literature are classed together, for the 

 most part incorrectly, under the name of nucleoli, show material 

 differences amongst themselves. This has been proved beyond a 

 doubt by the investigations made by Flemming (II. 10), Carnoy 

 (II. 8), myself (II. 19a), Zacharias (II. 45), and others. Either 

 such very different bodies should not be called by the same name, 

 or if, merely on account of their similarity in form, the common 

 name of nucleolus or nuclear body is retained for all round nuclear 

 contents, at any rate in each case an accurate description of the 

 chemical nature of the nucleolus in question should be given. 

 Above all, as has been already remarked, in all examinations of the* 

 nucleus, more attention should be .paid to the chemical properties, 

 of its individual constituents than to their form and arrangement, 

 which are always of comparatively little importance. For the 

 function of a framework in the nucleus composed of linin threads, 

 differs considerably from that of one consisting of nuclein, or of a 

 combination of the two substances, and similarly the function of the 

 nucleolus varies according to the material of which it is composed. 



I will conclude this discussion of nucleoli with the remark that 

 germinal spots exist which are most evidently built up of two 

 different substances. This circumstance was first observed by 

 Leydig in a lamellibranchiate Mollusc, and his statement has since 

 been verified by Flemming (II. 10) from observations on the same 

 animal, and by myself (II. 19) from those on other objects. I here 

 quote the description as it is given by Flemming. 



