Dbcembee 1, 1922] 



SCIENCE 



635 



SPECIAL ARTICLES 



ORGANIZATION OF HETEROTYPIC 



CHROMOSOMES 



In a recent article H. C. Sands^ gives a pre- 

 liminary account of his interpretation of 

 ekromosome structure in Tradescantia. This ac- 

 count seems to differ much in fundamentals 

 from the results of a study conducted by the 

 writer on various species of the South African 

 Liliaceous genus Gasteria. To consider only 

 the most interesting feature, the heterotypic 

 chromosomes, we find first that at metaphase 

 there are three pairs of sm;all iChromosomes in 

 the center of the plate, with four pairs of much 

 larger ones arranged in radiating fashion 

 ■around them. In favorable material it is easy 

 tx) see that the metaphase chromosomes are 

 organized internally into chromomeres, though 

 these are somewhat irregularly arranged. Even 

 before they separate the larger chromosomes 

 each show a cleft at the outer end opposite the 

 fiber attachment, and before anaphase is far 

 advanced they are nearly completely divided 

 longitudinally into two halves. Usually this is 

 entirely completed before telophase sets in, 

 and the halves are widely separated. The 

 smaller chromo'somes are slow to split, but 

 finally do so. Consequently there is at telo- 

 phase a diploid number of separate chromo- 

 Some-halves and the homotypie division has 

 been prepared for. 



As the larger chromosomes separate in ana- 

 phase it is clear that in each half-chroinosome 

 there is a double row of rounded ohromomeres. 

 These are few and apparently quite definite 

 in number, well separated from each other 

 and stain sharply in contrast to the almost 

 colorless matrix. As the membrane first ap- 

 pears around the group of telophase chromo- 

 somes (which are well separated in this genus 

 and easily studied) it becomes evident that 

 there are no longer two rows of chromomeres, 

 but that four are now ipresent. When the 

 chromosomes are obliquely placed these can 

 clearly be distinguished, especially in the later 

 stages when the chromosomes begin to broaden 

 at the ends in preparation for a more even dis- 

 tribution of the chromatin in the interkinetic 

 nucleus. The smaller roundish chromosomes 



1 Sands, H. C. : " Perigenesis, ' ' Science LVI, 

 517-518, 1922. 



show comparable changes, though less clearly 

 because of their size. It would seem that this 

 can only mean that both the gametophyte divi- 

 sions in the pollen grain have been completely 

 prepared for. The chromomeres which enter 

 the construction of the sperm nuclei seem to be 

 already formed and merely awaiting the me- 

 chanical distribution of these mitoses. Unfor- 

 tunately it has not been possible to trace the 

 history of .the ohromomeres as such through 

 these two divisions. 



By a method based on smear preparatiens 

 it has been possible to largely confirm the re- 

 sults of sectioned material and to obtain fixa- 

 tions in which synizesis (synapsis) has been 

 almost entirely eliminated. The best results on 

 tiie anaphase and telophase stages were ob- 

 tained when the dividing cells were iDressed 

 from the anther before fixing and embedding. 



The writer would consider, then, that the ma- 

 terial worked upon, Gasteria, tends to demon- 

 strate a very great precision in the chromo- 

 mere constitution of the meiotie chromosomes. 

 It is hoped that it will be possible soon to make 

 a. full report giving the evidence for the views 



here expressed. „^ 



Wm. Randolph Taylor 



University op Pennsylvania 



THE INTELLIGENCE OF INDIANS 



The accompanying tables show that if we 

 rank mixed bloods of certain heredity with no- 

 madic and sedentary full blood Indians accord- 

 ing to intelligence as indicated by Scale A of 

 National Intelligence Tests the sequence proves 

 to be : 



L Mixed Bloods. 



II. Mexicans. 



III. Plains and South Eastern Full Bloods. 



IV. Plateau Indians, Full Bloods. 



V. Navajos and Apaches, Full Bloods. 



While the number of cases is small the indica- 

 tions of the measures are consistent with this 

 inference. The results will shortly be reported 

 more in detail by the writer who has been giv- 

 ing these tests in United States Indian Schools 

 of the Southwest. 



THE RELATIVE INTELLIGENCE OF INDIANS OP NO- 

 MADIC AND SEDENTARY TRIBES AND MIXED 

 BLOOD INDIANS 



The scores are of the National Intelligence 

 Tests, Scale A, Form 1. 



