. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. According to my interpretation of the Vierergruppen in Calopte- nns, the formula would be -j a , > . Both the divisions following the formation of a Vierergruppe would therefore be reductions, and it would be quite immaterial whether the first di- vision gave rise to two cells a b and c d, or to the two cells a c and b d. In Calop- tenus the rings may be placed upon the spindle equator in either of the two posi- tions l'epresented in Diagrams 1 and 2. This offers, perhaps, an explanation and reconciliation
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. According to my interpretation of the Vierergruppen in Calopte- nns, the formula would be -j a , > . Both the divisions following the formation of a Vierergruppe would therefore be reductions, and it would be quite immaterial whether the first di- vision gave rise to two cells a b and c d, or to the two cells a c and b d. In Calop- tenus the rings may be placed upon the spindle equator in either of the two posi- tions l'epresented in Diagrams 1 and 2. This offers, perhaps, an explanation and reconciliation of the contradictory views of Henking, Hertwig, Hacker, and others. As has been said, Henking holds that the first division is a reduction division, and the second an equation division, while most authors make the first an equation, and the second a reduction division. Henkiug ('91) did not, in his Pyrrhocoris paper, recognize the existence of Vierergruppen as a regular stage in maturation; but I feel justified by his Figure 20 in believing that they were really present in Pyrrhocoris, just as in Gryllotalpa, Caloptenus, etc. Now, supposing the proper formula for the Vierergruppen to be ] , , [, why might it not happen in dif- ferent nuclei, or in different chromatic groups of the same nucleus, that one group should divide thus, —, and another thus, , , 1 Henking must assume that all the gi-oups are arranged on the spindle so as to separate the non-identical idants by the first division. Hacker says : " In der zweiten Richtungstheilung erfolgt dann die definitive Trennung der nichtidentischen ; The following diagrams may illustrate these positions : — I. a a b b II. III. a b a a a1 P • • • • • • • • • • • • a b b b a1 b1 Diagram I. illustrates Henking's view of the first division interpreted according to the scheme of the Vierergruppen. All the groups would thus suffer reduction Please note that these images are ext
Size: 993px × 2518px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorha, bookcentury1800, bookdecade1860, booksubjectzoology
