228 



INTRODUCTION TO CYTOLOGY 



a transverse division of the chromosome nor a transverse separation of 

 bivalents? Montgomery (1901), von Winiwarter (1900), Button (1902), 

 Boveri (1904), and a number of others showed that here the chromo- 

 somes conjugate side-by-side rather than end-to-end. Thus when they 

 separate there is an appearance of a longitudinal division, but reduction 

 is nevertheless accomplished, since entire somatic chromosomes suppos- 

 edly qualitatively different, and not the longitudinal halves of split 

 chromosomes, are separating. The appearance of a longitudinal division 

 may also be present after an end-to-end conjugation, for the two members 

 may bend around to a side-by-side position before finally separating. 



FIG. 81. Diagram showing essential difference between somatic and heterotypic 

 mitoses. 



As a matter of fact, the maturation divisions in nearly all cases, especially 

 those studied by botanists, are both longitudinal in appearance. End- 

 to-end conjugation later came to be called telosynapsis or metasyndese, 

 and side-by-side conjugation parasynapsis or parasyndese. 



Somatic and Heterotypic Mitoses Compared. Before taking up a 

 more detailed account of the process of reduction as it has been described 

 by various investigators it is of the utmost importance to fix clearly in 

 mind the essential difference between somatic and heterotypic mitosis 

 in order to realize what constitutes the cardinal feature of reduction, and 

 thereby to detect the significant points of the various theories. This 

 essential difference is illustrated in Figs. 81 and 82. In a somatic or 

 vegetative mitosis every chromosome is split into two exactly similar longi- 

 tudinal halves which are distributed to the two daughter nuclei. The daughter 

 nuclei are therefore like each other and like the mother nucleus in the quality 



