THE REDUCTION OF THE CHROMOSOMES 



249 



parasynaptically rather than two split ones placed end-to-end. In 

 support of this contention he cites the following observations: such 

 "tetrads" are seen not only in the oocytes and spermatocytes but also in 

 oogonia, spermatogonia, and somatic cells; the supposed telosynaptically 

 conjugated members are often very unequal in size; such tetrads are 

 sometimes divided in the transverse plane at neither maturation mitosis ; 

 not only tetrads, but also octads and hexads are often observed, even in 



FIG. 98. Chromosome tetrads. 



A, five stages in the development of the tetrad in the spermatocyte of Anasa tristis. 

 X 3000. From a preparation by Dr. H. E. Stork. B, tetrads in sporocyte of Chiloscyphus. 

 Enlarged; X 2800. (After Florin, 1918.) C, tetrads in Richardia africana. (After 

 Overton, 1909.) D, false tetrads in somatic cells of Pisum due to action of chloral hydrate 

 on constricted chromosomes. (After Sakamura, 1920.) 



the same cell, and these are plainly due to the presence of additional 

 accentuated constrictions. Robertson (1916) also interprets such telo- 

 synaptic rod tetrads as those observed by Haecker in the copepods as 

 constricted chromosomes. The constrictions, according to this writer, 

 represent points of temporary union between non-homologous elements. 

 From these considerations it is evident that constrictions have much to 

 do with the appearances assumed by chromosomes, and that they should 

 be taken into account in interpreting the chromosome tetrad. 



Numerical Reduction Without Qualitative Reduction. Figure 99 

 illustrates the behavior of the chromosomes in maturation according to 

 three not widely accepted views. A few workers, including Fick (1907, 



