“McClung fait grand fond, pour appuyer son interprétation, sur une forme spéciale, la forme en anneau, qui pour lui dérive du bâtonnet a′ b′
a′ b′’, supposé placé transversalement sur le fuseau, inséré par son milieu et incurvé en dehors jusqu’ à rapprochement et soudure de ses extrémités.
“Le chromosome en anneau est en effet très fréquent chez les acridiens; mais il nous a été possible d’en reconstituer l’histoire, grâce à des détails qui ne semblent pas s’être rencontrés dans les figures de McClung. On se souvient que nous avons établi les deux points suivants en complet désaccord avec la théorie de l’auteur américain:
“1. Les deux moitiés de l’anneau proviennent de la première division longitudinale.
“2. L’insertion est terminale.”
With equal emphasis, I must deny that the enclosed space in the ring represents any plane of division in the chromatin thread; and that the insertion of the spindle fibers is at any place except at the center of what would be the typical rod-shaped chromosome were the ring straightened out. We encounter in de Sinéty’s interpretation of these rings the very error against which I was careful to caution elsewhere in this paper, i. e., of regarding the points where the fibers are attached as the crossed ends of a simple segment. This mistake de Sinéty has made, and has thereby vitiated all his conclusions concerning the structure of the tetrads. It is not necessary to repeat here the proof which I have brought forward in support of my views. No one, I am sure, will find difficulty in reducing the various forms of chromosomes found in the first spermatocytes to the type of a doubly split rod, in which one plane of division is parallel to the long axis and the other at right angles to it. The explanation offered by de Sinéty requires us to conceive a doubly split rod in which one separating space may vary indefinitely while the other is constant. There is here no common type, but an infinitely variable one, which differs with every modification of the interspace between the first pair of chromatids in each chromosome.
As a constructive basis for the foundation of his theory of a double longitudinal division, de Sinéty uses particularly the chromosomes of Œdipoda (Hippiscus) miniata, represented in figures 129 and 130, concerning which he says:
“Survient le phénomène exceptionnellement important de la seconde division longitudinale; nous regardons comme un point capital dans notre travail d’en mettre l’existence hors de doute et pour cela nous désirons ne faire appel qu’à des images extrêmement claires. Nous considérons comme telles les fig. 129 et 130 rapprochées l’une de l’autre.
“Il est de toute évidence que le chromosome a, fig. 130, n’est que le chromosome de même désignation, fig. 129, dont les deux anses jumelles se sont clivées. De même, le chromosome en forme de boucle, c, fig. 129, dont les deux branches représentent, comme nous l’avons fait remarquer, deux anses jumelles, se retrouve avec un clivage très évident en d, fig. 123. On pourrait faire les mêmes rapprochements entre b, fig. 105, et a, fig. 107; ici, le clivage est moins avancé, mais les granules sont nettement divisés.”
I am obliged to confess that I have never seen in other species of this genus any appearances that would incline me to place an interpretation upon them such as does our author upon these. I would venture to suggest, on the contrary, that the chromosomes represented in figure 129 have not as yet demonstrated any division, but show merely irregular spaces between chromosomes. At even an earlier stage (figs. 5, 37, and 38), I have shown the formation of the tetrads by means of simultaneous cross and longitudinal divisions so clearly that presumed successive divisions, as represented by de Sinéty, cannot be regarded as occurring.
Finally, I would emphasize the fact mentioned in connection with the discussion of the cross-shaped chromosomes, that where the elements of one of these compound chromosomes intersect they lie in one plane, and are not superimposed upon each other, as de Sinéty’s theory demands and as his figures represent. This was shown clearly in Paulmier’s figures as well as in my own, and is even more clearly demonstrated, if possible, in the very long, slender chromosomes of the myriapods, which I have observed in Mr. Blackman’s preparations. This, and the continuity of the chromatin in contiguous arms of the cross, is alone sufficient to disprove de Sinéty’s theory, and, fortunately, is easily demonstrated. This same fault of de Sinéty’s is encountered, in another form, in his discussion of the ring figures. He asserts that the halves of the rings are pulled past each other while they lie in the plane of the spindle axis. Herein my observations fail entirely to agree with his. The rings lie in the plane of the equator, and no elements of the mitotic figure show a lateral displacement of the separating halves equal to the width of the chromosome when viewed in this plane.