MATURATION. 29 



the hypotheses have received support from observation, others are still hypotheses in the 

 strictest sense of the word. 



Some of the earlier investigators interpreted reduction merely as a means to prevent the 

 summation of the nuclear mass in succeeding generations, or in other words, as a means to 

 prevent the doubling of the number of chromosomes in each succeeding generation. For 

 if there were no reduction, the egg cell and the sperm cell each would bring to the segmenta- 

 tion nucleus the full amount of chromatin or the somatic number of chromosomes. This 

 would result in the doubling of the chromatin mass at each fertilization. While reduction 

 does, as a matter of fact, prevent this summation, the inadequacy of this explanation is 

 apparent when one considers that in the vast majority of cases the mass reduction is not 

 one-half but three-fourths, and furthermore that mass reduction really means but little 

 because the bulk of the nuclear substance may increase or decrease enormously at different 

 periods in the life history of the cell. 



Another interesting view first held by Minot, and later adopted by others, was that the 

 ordinary cell is bisexual or hermaphroditic, and that maturation is an effort on the part 

 of the germ cells to rid themselves of the opposite sexual elements, i.e., the ovum rids itself 

 of its male elements to become a true female sex cell; the spermatozoon of its female 

 elements, to become a true male sex cell. This theory also met with a serious objection 

 when it was found that four functional spermatozoa are derived from a single primary 

 spermatocyte. The fact that female qualities are transmitted by the male germ cell and male 

 qualities by the female germ cell is also opposed to this theory. 



The most modern theory is extremely complex and is closely associated with, even forms 

 a part of, the modern ideas of inheritance. Weismann first, in 1885, considered the deeper 

 meaning of reduction and set forth his views in an article of highly speculative character, 

 but which gave great stimulus to further study of the problem. Weismann's first assump- 

 tion was that " Chromatin is not a uniform and homogeneous substance, but differs quali- 

 tatively in different regions of the nucleus; that the collection of the chromatin into the 

 spireme thread and its accurate division into halves is meaningless unless the chromatin in 

 different regions of the thread represents different qualities which are to be divided and 

 distributed to the daughter cells according to some definite law." He argued that if the 

 chromatin were the same throughout, mitosis would be superfluous and direct cell division 

 would be sufficient. The real starting-point of Weismann's theory is that the chromatin is a 

 colony of minute particles — biophores — each of which has the power of developing some 

 quality. The biophores are grouped together into larger masses or determinants, and the 

 latter are grouped to form ids. The ids are identified with the visible chromatin granules. 

 Each id is assumed to possess potentially the complete architecture of the species, i.e., each 

 id has the power of determining the development of all the qualities characteristic of the 

 species. The ids differ slightly from one another according to individual variations within 

 the species, and are arranged in a linear manner to form the chromosomes. Thus each 

 chromosome is a group of slightly different germ-plasms and differs qualitatively from all 

 others. 



The interpretation of these hypotheses and their formulation into a theory leads to still 

 greater complexity. If there were no reduction and each germ nucleus brought to the 

 segmentation nucleus the full amount of chromatin, the number of chromosomes would be 

 doubled and consequently the number of ids. And since each id has the power of deter- 

 mining the development of all the qualities of the species, an infinite complexity would arise 

 after a few generations. By reducing the ids both in size and in number in each germ cell, 

 the tendency toward this infinite complexity would be held in check. Thus on the assump- 



