REDUCTION WITHOUT TETRAD-FOKMATION 26/ 



second division the limbs of the daughter-V's again come close 

 together, remaining, however, united at one end, where they were 

 believed finally to break apart during the second division. The latter 

 was, therefore, regarded as a true reduction-division, the apparent 

 longitudinal split being merely the plane along which the halves of 

 the V come into contact (Fig. 134, C, D). 



The two accounts just given represent two extremes, the first 

 agreeing essentially with Ascaris, the second with the copepods or 

 insects. When we compare them with others, we encounter a truly 

 bewildering confusion. Strasburger and Mottier ('97) themselves 

 soon abandoned their acceptance of the reducing division, returning 

 to the conclusion that in both sexes {Liliiuu, Podophyllmn) both divi- 

 sions involve a longitudinal splitting of the chromosomes (Figs. 133, 

 134). In the first division the longitudinally split spireme segments 

 into twelve double rods, which bend at the middle to form double V's, 

 with closely approximated halves. Becoming attached to the spindle 

 by the apex, the Umbs of each separate to form a -figure. At 

 telophase the daughter-V's shorten, thicken, and join together to form 

 a daughter-spireme consisting of a single contorted thread. TJiis 

 splits IcngtJnvise throughout its wJiolc extent, and then segments into 

 double chromosomes, the halves of which separate at the second 

 division (Fig. 135, L-]\I). The latter, therefore, like the first, 

 involves no reducing division. This result agrees in substance with 

 the sHghtly earlier work of Dixon ('96) and of Miss Sargant ('96, 

 '97), whose account of the origin of the o -figure of the first division 

 differs, however, in some interesting details. It is also in harmony 

 vi^ith the general results of Farmer and Moore ('95), of Gregoire ('99), 

 and of Guignard ('98), who, however, describes the first division nearly 

 in accordance with Strasburger's account of 1895, as stated above. 

 On the other hand, Ishikawa (pollen-mother-cells of Allium, '97) and 

 especially Belajeff (pollen-mother-cells of Iris, 98) conclude that the 

 second division is a true transverse or reducing division. ^ Ishikawa 

 described the first division as being nearly similar to the ring-forma- 

 tion in copepods, the four elements of the ring being often so 

 condensed as nearly to resemble an actual tetrad. In the early ana- 

 phases the daughter-V's break at the apex ; and, although in the later 

 anaphases the limbs reunite, Ishikawa is inclined to regard the trans- 

 verse division as being a preparation for the second mitosis. Bela- 

 jeff's earlier work ('94) on Z ///;/;;/ gave an indecisive result, though 

 one on the whole favourable to a reducing division. In his latest 

 paper, however ('98, i ), Belajeff takes more positive ground, stating 

 that after the examination of a large number of forms he has found 



1 Schaffner ('97, 2) reaches exactly the reverse result in Lilium philadelphicum, i.e. the 

 first division is transverse, the second longitudinal. 



