CRITICISMS AND CONCLUSIONS. 



S3 



although Gerlach (1906, p. 13) believes that the typical forms appear in 

 the prophase only and that, apparently as a result of shrinkage, the 

 chromosomes of the equatorial plate are short, rounded rods, like those 

 of the second spindle. This supposed change of form is explained when 

 it is noted that in Gerlach 's figures the chromosomes of the first spindle 

 of ovarian eggs (Gerlach 1906, Taf. 1, fig. 2, 3) have the typical forms, 

 while the oviducal egg (fig. 4) with supposed first spindle has the rod- 

 like chromosomes; for, as pointed out before, what he calls first spindles 

 in oviducal eggs are really second spindles. Therefore, Gerlach's ma- 

 terial, after all, presents no real exception. 



Gerlach (1906, p. 25) regards the chromosomes of the first spindle 

 as tetrads, those of the second as dyads. The conclusion that the chro- 

 mosomes of the first spindle are tetrads is based entirely on indirect 

 evidence and on reasoning from analogy with conditions demonstrated 

 in many invertebrates. Since in the first polar cell he finds that the 

 chromosomes sometimes seem to be present as dyads, he reasons that 

 those of the first maturation spindle must have been tetrads. 



None of these observers has recognized and figured the quadripar- 

 tite structure of the chromosome of the first maturation spindle. Both 

 Tafani and Gerlach (1906, pp. 13-14), it is true, state that the chromo- 

 somes are composed of Pfitzner's granules embedded in a less deeply 

 stainable substance ; but that has no bearing on the question of quadri- 

 partite structure. That the first division is transverse is believed by all 

 authors except Tafani (1889, p. 22), who thinks it longitudinal, though 

 he has not directly observed it in the mouse. But, since he confused 

 the two spindles with each other, this statement applies to the second 

 spindle only. Sobotta (1899, 1907) alone gives illustrations of migrating 

 daughter chromosomes; but in none of his figures does he show their 

 longitudinal division. There is no doubt, as both Sobotta (1907, p. 511) 

 and Kirkham (19076, p. 73) state, that some chromosomes divide earlier 

 than others. 



When one examines carefully the accounts of the first maturation 

 spindle given by Sobotta (1895, I 9 7)> ft * s evident that in his first paper 

 he speaks of a relatively early stage (fig. 4a) of the spindle as showing 

 the equatorial plate, a stage which he later designates correctly as the 

 prophase. Subsequent writers — Gerlach, Kirkham — have figured simi- 

 lar stages, and Kirkham (19076, p. 73, fig. 2) has applied the expression 

 equatorial plate even to a stage in which the chromosomes are distrib- 

 uted over half the length of the spindle. Gerlach (1906, p. 13), however, 

 clearly states it as his opinion, and in this we believe he is right, that 

 such spindles are still in process of formation; but, in our opinion, he 

 fell into an error in ascribing to a later stage of the first spindle a condi- 

 tion which is to be found only in the second maturation spindle ; for he 

 says that when the equatorial plate is fully formed it presents in the side 

 view of the spindle a fairly uniform appearance, its chromosomes having 



