THE HETEROTYPIC MATURATION MITOSIS 



IN AMPHIBIA AND ITS GENERAL 



SIGNIFICANCE. 



THOS. H. MONTGOMERY, JR. 



The marked contradiction between the results of workers on 

 spermatogenesis of vertebrates, and of those on the spermato- 

 genesis of arthropods, has led me to examine the formation of 

 the chromosomes of the first maturation mitosis in urodele am- 

 phibia. The question at issue is of course the interpretation of 

 the heterotypic division, for if that is an equational division as 

 generally maintained, then in vertebrates there would be no trans- 

 verse, or so-called " reduction," division of the chromosomes. 

 Much time and thought has been given to the interpretation of 

 the various ring-shaped chromosomes of heterotypic, divisions, 

 /. e., as to whether the space enclosed by the ring represents a 

 longitudinal split of a single chromosome, or a space between 

 two univalent chromosomes. Uncertainty and confusion has 

 resulted, because most of these interpretations have not taken 

 into account the earliest stages in the formation of such chro- 

 mosomes, which are really the only stages that need critical 

 examination. 



The two species in which these decisive periods of the sperma- 

 togenesis was studied, are Plctliodon cincreus (Green) and Des- 

 mognathus fuscus (Raf.); the maturation mitoses occur in the 

 summer, and the testes were fixed in Hermann's and Flemming's 

 solutions, and stained with iron hsmatoxyline. The spermato- 

 genesis is essentially alike in both ; Figs. I 6 are camera drawings 

 of spermatocytes of Desmognatkus, and 7 and 8 of Plethodon. 



The normal number of chromosomes is twenty-four as shown 

 clearly on a pole view of a monaster (equatorial plate) stage 

 (Fig. i) ; in this figure four of the chromosomes are cross-sec- 

 tioned, and one of the others shows very clearly the longitudinal 

 split. In the spermatocytes which result from the last sperma- 

 togonic division there is just half this number of chromosomes, 

 namely twelve, the so-called reduction in number taking place 



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