260 INTRODUCTION TO CYTOLOGY 



variety of agencies, including chloral hydrate, benzene vapor, ether, chlo- 

 roform, and the gall-producing secretions of Heterodera, may be employed 

 to bring about aberrations of the mitotic process. After the chromosomes 

 are divided and partially distributed they may be reorganized in a single 

 "didiploid" nucleus. In other cases the chromosomes may reorganize 

 as two or more nuclei with various chromosome numbers, and these may 

 often fuse to form " syndiploid " nuclei. To all the kinds of stimuli applied 

 the chromosomes react by becoming shorter and thicker, and thus appear 

 like heterotypic chromosomes. Furthermore, latent or obscure constric- 

 tions are rendered more conspicuous, so that some of the split chromo- 

 somes appear like chromosome tetrads. Sakamura shows that these false 

 tetrads do not represent heterotypic phenomena in any true sense : they are 

 merely the result of the response of split and constricted chromosomes to 

 the abnormal conditions induced in the cell, and have nothing to do with 

 any reducing process. No such autoregulative reduction occurs in these 

 didiploid cells, their gradual decrease in relative number being due to 

 their lowered capacity for, and rate of, division. 



Child (1915) emphasizes the physiological significance of maturation, 

 and shows that the heterotypic phenomena are associated with a low 

 metabolic rate in the cells, that they may occur occasionally in other cells 

 having a low rate, and that they can be induced artificially with narcotics 

 as Nemec stated. 



All of these observations are interesting in that they indicate the 

 nature of some of the physiological changes occurring at the time of matur- 

 ation. The description of the heterotypic phenomena upon which will 

 be based our ultimate interpretation of its significance, will not be com- 

 plete until the physiological as well as the morphological changes have 

 been exhaustively examined and correlated. But because it has been 

 found that the onset of the meiotic process is associated with a lowering of 

 the rate of metabolism which, if continued, may result in degeneration; 

 or because appearances similar to those of the heterotypic prophase may 

 occur in other cells with disturbed metabolism; it does not at all follow that 

 the heterotypic phenomena are at bottom phases of a degeneration 

 process, or that they have no other significance in the normal life cycle. 

 These phenomena occur almost universally throughout the whole world 

 of living organisms at a very critical stage in the life cycle and lead to 

 significant results with a high degree of regularity. The lowered rate of 

 metabolism accompanying them offers in the vast majority of cases no 

 check to the normal functioning of the products of the maturation di- 

 visions. It therefore seems more reasonable to regard the observed 

 degeneration as a secondary effect that may occasionally set in during the 

 normal heterotypic prophases because the metabolic rate is already at a 

 relatively low level at that time, than to look upon the heterotypic 

 changes as a part of a degeneration process which is only exceptionally 



