xiv] ELIMINATION OF CHROMOSOMES 211 



chromosomes twenty-one or twenty-two chromosomes are 

 found in the subsequent mitoses. BALTZER believes that the 

 eliminated chromosomes are all paternal (from Sphaerechi- 

 nus), chiefly on the grounds (i) that Sphaerechinus has two 

 long straight chromosomes and Strongylocentrotus a long 

 hooked one, and that in the hybrid embryos the straight 

 chromosomes are never present while the hooked one always 

 is; and (2) in a quadripolar spindle derived from a di- 

 spermic egg there are only a few (about four) more chromo- 

 somes behaving normally than in an ordinary mitosis, while 

 if the paternal chromosomes behaved normally there would 

 be twenty extra. Nearly all the embryos become abnormal 

 in the gastrula stage, and die off, but in the very rare cases 

 in which plutei have been reared these were of the maternal 

 type. If the eliminated chromosomes are paternal, their 

 absence would thus account for the lack of paternal char- 

 acters in the hybrid, while in the converse cross no chromo- 

 somes are eliminated and the hybrid pluteus shows the 

 characters of both parents. Similar elimination of chromo- 

 somes has been observed by Miss PINNEY in Teleostean 

 hybrids. 



Further evidence in favour of the hypothesis that the 

 chromosomes are of especial importance in determining 

 inherited characters has been obtained from plants. In 

 Oenothera (Evening Primrose) at least two species have a 

 variety known as lata, in which the leaves are broader than 

 in the type form, and these lata varieties have one more 

 chromosome than the normal, the typical number being 

 fourteen while lata has fifteen. Since one chromosome is 

 unpaired, various irregularities arise in the maturation 

 divisions of the germ-cells; the unpaired chromosome may 

 go over undivided to one pole in the heterotype division, 

 and divide equationally in the homotype, so giving equal 



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