THE ZOOLOGICAL STATION AT NAPLES. 285 



basi-chromatin : l)oth constituents stain black. Its chief use is for differ- 

 entiating the nucleolus from the chromatin. This is what iron-hcema- 

 toxylin, for example, does not do. 



The results of staining sections of the fixed ova of Tomopteris were as 

 follows : — 



Iron haimatoxylin and orange G. varies a good deal, according to the 

 time allowed for extraction of tlie stain with iron-alum. After a Ion"- 

 extraction primitive spireme, nucleolus, and definitive chromosomes, black. 

 Oxychromatin, orange. Cytoplasm, purple. Yolk spheres and zymoo-en 

 granules of gut cells, pale. 



Delafidds hn-matoxylin and eosin. — Nucleolus, brick red. Chromatin 

 blue to light red, according to age of oocyte. 



Borax-carmine and picro-nigrosin. — iSTucleolus and definitive chromo- 

 somes, bright red. Remaining nuclear contents, purple. 



Nigrosin and light green. — Nucleolus, green. Chromatin, black. 

 Cytoplasm, green. 



It will thus be seen that with certain combinations of dyes nucleolus 

 and 'basi-chromatin ' stain alike, whereas other double stains differentiate 

 these two constituents of the nucleus. The result is rather conflicting. 



The precise origin of the nucleolus or germinal spot could not be 

 made out. It is present when the chromatin is in the spireme stage and 

 the nucleus has as yet no definite membrane. When the membrane is 

 formed the nucleolus is applied to its inner surface, and has one side 

 flattened against the latter. As the egg grows the nucleus leaves the 

 wall and lies eccenti'ically within the nucleus. It is invariably surrounded 

 by a vacuole, to the walls of which it is moored by threads of the nuclear 

 reticulum. The progressive vacuolisation of the germinal spot has been 

 already referred to. 



The large eccentric vacuole of the germinal spot owes its origin 

 apparently to the fusion of numerous smaller vacuoles. When this fusion 

 is complete the germinal spot has attained its greatest size. The single 

 large vacuole — in stained sections — contains a reticulum with granules 

 staining exactly like the nuclear reticulum, although no communication 

 between tlie vacuole and the contents of the nucleus could be certainly 

 demonstrated. This vacuole with its contained reticulum corresponds 

 to what certain authors call the plastin portion of the nucleus and to the 

 'nebentheil ' (Flemming ') of the nucleus of the Lamellibranch egg. The 

 reticulum looks exactly like an included portion of tlie general nuclear 

 reticulum. It may, however, be due to the coagulation of the intra- 

 vacuolar fluid. 



The germinal spot or chief nucleolus of the oocyte of Tomopteris is 

 certainly not a karyosome ; neither is it a chromatin nucleolus in Carnoy's 

 sense ; that is to say, it has no genetic relation to the chromosomes or 

 ' nucleinkorper ' as have the numerous nucleoli of the germinal vesicle of 

 Amphibia and Fishes (according to Carnoy - and Rohde '^). Further, there 

 appears to be no difference, as regards staining properties and morpho- 

 logical relations, between the germinal spot of the egg and the nucleolus 



' Flemming, Zellsvhstanz, Kern und Zelltlwilung, 1882, &c. 



2 Carnoy et Lebrun, ' La vt'sicule germinative et les polaires globules chez leti 

 Batrachiens,' La Cellule, 12, 14, 17. 



' Eohde, ' Ueher den Bau der Zelle, i. Kern und Kernkorper,' Zeit. fiir niss Zonl 

 Bd. Ixxiii., Hft. 4, 1903. " ' 



