PECULIARITIES OF REDUCTION IN THE INSECTS 2/1 



Resume. In reduction without tetrad-formation the spireme seg- 

 ments into half the somatic number of chromosomes, which split 

 lengthwise and open out to form rings for the first (heterotypical) 

 mitosis. According to one set of observers, including Flemming, 

 Meves, McGregor, Kingsbury, Moore, Klinckowstrom, Van der Stricht, 

 Francotte, Griffin, Belajeff, Farmer, Dixon, Strasburger, Sargant, 

 Mottier, Ishikawa, and Atkinson, the ring arises by a single longi- 

 tudinal division. According to another group, including Carnoy, 

 Le Brun, Guignard, and Gregoire, the ring arises through a double 

 longitudinal division, one representing the axial and the other the 

 equatorial plane of the <> -figure. The second group of observers 

 regard both maturation-divisions as longitudinal. Among the first 

 group, Flemming, Meves, McGregor, Kingsbury, Moore, Farmer, 

 Dixon, Strasburger, Sargant, and Mottier likewise believe both divi- 

 sions to be longitudinal, the daughter-V's or their products again 

 splitting lengthwise for the second division ; while Klinckowstrom, 

 Van der Stricht, Francotte, Grififin, Belajeff, Ishikawa, and Atkinson 

 believe one of them to be transverse, the daughter-V's breaking apart 

 at the apex, and thus giving the reducing division of Weismann.^ 



D. Some Peculiarities of Reduction in the Insects 



We may here briefly consider some interesting observations which show that in 

 some cases the nuclear substance may be unequally distributed to the germ-nuclei. 

 Henking ('90) discovered that in the second spermatocyte-division of Pyrrocho- 

 ris one of the '• chromosomes " passes undivided into one of the daughter-cells 

 (spermatids) which receives twelve chromatin-elements while its sister receives but 

 eleven. (The number of chromosomes in the spermatogonia, and of rings in the 

 first spermatocyte-division is twenty-four) . This anomalous process is confirmed 

 with interesting additional details by Paulmier ('99) in Anasa, and obviously related 

 phenomena are described by Montgomery ("99, i ) in Pentaioi/ia, and by McClung ("99) 

 in Xiphidiiun. 



breaking apart of the V's at the apex, as described by Belajeff, is, therefore, not a transverse 

 division, but merely the completion of the second longitudinal division. (2) In a second 

 and exceptional type, the chromosomes are placed tangetitially to the spindle, and the 

 halves separate from the middle, again producing -shaped figures. These, however, are 

 not of the same nature as those arising in the first case, since they are formed by a bending 

 out of each daughter-chromosome at the middle to form the V, and not by the second longi- 

 tudinal split. The effect of the latter is in this case to render each daughter-V in itself 

 double, precisely as in the salamander. The difference between the two types results 

 merely from the difference of position of the chromosome with respect to the spindle, and 

 the final result is the same in both, i.e. two longitudinal divisions and no reducing one. 



This highly important work brings very strong evidence against the occurrence of trans- 

 verse or reducing divisions in the higher plants, and seems to explain satisfactorily most of 

 the differences of interpretation given by other observers. It will be interesting to see 

 whether a similar interpretation is possible in the case of moUusks, annelids, and arthropods, 

 where the early stages, in many cases, so strikingly resemble those occurring m the plants. 



^ Cf. footnote on page 269. 



