THE INTERPHASE NUCLEUS 



because it appears that the Amphibian germinal vesicle has a parti- 

 cularly high permeability. Both salts (Abelson and Duryee;!'^ Cal- 

 LAN^'^) and sugars (Callan^^^) are able to traverse it, whereas the 

 osmotic properties of other nuclei suggest that they are permeable to 

 water and not to solutes. Among these are Amphibian epithelial nuclei 

 (Hamburger^'*) and the germinal vesicle in the egg o^Arbacia punctulata 

 (Beck and Shapiro ;i^^ Churney^^^).* 



It is probable that various cells differ widely from each other in this 

 respect. It does not appear from the photographs of ZollingerI'^ 

 that the nucleus of cells in tissue cultures swells when distilled water is 

 added to the medium; Monne^^'' observed a transitory vital staining of 

 the nucleus in Amoeba when dyes were injected into the cytoplasm. In 

 these experiments acidic dyes penetrated the nuclear membrane more 

 rapidly than did basic ones. 



size of the interphase nucleus and of the chromosomes 



Not all the nuclei in one type of cell in an individual are of the same 

 size. Generally, the size of the nucleus is related to that of the whole 

 cell, and most of the literature of this subject is concerned with this 

 proportionahty, to which Hertwig (R.)i^^ gave the well-known name 

 of 'karyoplasmic ratio'. On the theoretical developments associated 

 with this idea, the verdict of Wilson^^^ is that they were 'undoubtedly 

 carried too far', but in these days probably too little is heard of the 

 subject. However, interest in the nuclear size, per se, has survived in 

 respect to its relationship to the number and size of the constituent 

 chromosomes. The early observations bearing on this subject indicated 

 a close and fixed proportionality; but as one might expect, other factors 

 have since emerged which modify and complicate it. 



Production of haploid and tetraploid larvae in Echinoderms 

 The classical experiments in this field are those of Boveri^^" who 

 employed the methods discovered as early as 1887 by Hertwig (O. 

 and R.)i^i for the production of haploid and tetraploid larvae of 

 sea-urchins. If unfertilized eggs are suitably shaken, they can be separ- 

 ated into two parts, one with, the other without, the nucleus f; 

 these halves then round off and both can be fertilized and subsequently 

 undergo cleavage. The phenomenon was called 'merogony'. Both 

 diploid and haploid larvae result from this procedure, the chromosomes 

 of the latter being solely derived from the sperm nucleus. A tetraploid 

 larva can be produced by shaking a normal fertilized tgg near the time 



* Chambers and Pollack^'*^ found that phenol red penetrated into the germinal vesicle 

 of the starfish egg. 



t It is now customary to employ the centrifuge to effect this operation (Harvey**^). 



53 



