W. E. HOY, JR. 



i. e., physico-chemically, similar. This latter idea is further 

 developed, and he thinks that this assorting of the chromosomes 

 in pairs demonstrates a qualitative difference of the pairs. 



The view that the chromosomes may be the same in number 

 and type in all the cells of the body, or that fragmentation or 

 transverse splitting on the one hand, and fusion of pairs on the 

 other hand may account for differences is challenged by a number 

 of investigators, who believe that a limited degree of variation 

 may really occur (Barratt, Gutherz, Farmer and Moore, Delia 

 Valle, Rabl, Meves, Foot and Strobell). If there may be varia- 

 tion in the number of the chromosomes in various cells of the 

 same individual, it is certainly not of general occurrence, and no 

 really clear case has been presented. I believe that variation in 

 number is more often between individuals of the same species 

 than between cells or tissues of the same animal. Variations in 

 the size of chromosomes are more difficult of analysis, and more 

 difficult of demonstration. In Anasa it is clear that the chromo- 

 somes of any cell maintain the typical size relations, so that 

 particular pairs can be picked out with little trouble. The 

 results of Rabl and Meves are the reverse of this. Foot and 

 Strobell ('13) write: "We demonstrated in 1905 that the form 

 and relative size of the chromosomes in Allolobophora foetida are 

 inconstant and in every publication since that date we have 

 demonstrated variability in form, relative size and behavior of 

 the chromosomes in every form we have studied, and we have 

 consistently argued that such variability attacks the very founda- 

 tions upon which the popular chromosome speculations of this 

 decade have been built." 



Before many of these questions can be satisfactorily answered 

 detailed study must be made of the chromosomes in the somatic 

 cells of many more forms, especially where the somatic and gonial 

 numbers do not agree. Also a thorough review must be made 

 of the many apparently aberrant cases, which have been briefly 

 considered here. 



BIBLIOGRAPHY. 

 Agar, W. E. 



'n The Spermatogenesis of Lepidosiren paradoxa. Quart. Journ. Micr. Sci., 



Vol. 57- Pt. i. 



'12 Transverse Segmentation and Internal Differentiation of Chromosomes 

 Quart. Journ. Micr. Sci., Vol. 58. 



