348 BULLETIN OF THE 



dentate border caused by the unfused portions of the rods. By the 

 constriction and division of the cell the filaments are cut in the equa- 

 torial plane, and withdraw into the mass formed by the rods, now 

 completely fused. This mass is at first homogeneous, then small vacu- 

 oles appear, a membrane becomes perceptible at its periphery, and the 

 contents are resolved into rodlike corpuscles like those which the nucleus 

 contained before division. 



The nuclear equatorial granules were only rarely seen, and then they 

 took the place of the rods, each sending a filament to each pole of the 

 nucleus. They are only local accumulations of the substance of the rods, 

 which is withdrawn from the poles to be concentrated in the equatorial 

 region, — simple varicosities of the filaments. Balbiani was unable to 

 observe the radial phenomena of the cell protoplasm, on account, as he 

 thinks, of its great homogeneity. 



Mayzel ('76^) ^ distinguishes two forms of nuclear division in epi- 

 thelial and other tissues of numerous animals which he has studied. In 

 one form — constantly exhibited by the endothelium of the cornea (frog) 

 — there is a spindle-shaped structure, which is divided, he says, into 

 two cones by a median transverse nuclear disk ; from this nuclear plate 

 numerous fibres extend to the apices of the cones, quite the same as seen 

 by Strasburger and Biitschli in Blatta, etc. 



The rods and granules, however, which compose the nuclear disk do 

 not appear in Mayzel's preparations f as thickenings of the nuclear fibres, 

 but form, in some cases at least, a kind of ring surrounding the spindle, 

 the latter being composed of fibres alone. One may therefore assume, 

 I think, that the elements which form the nuclear disk arise from com- 

 pacted nuclear substance which is independent of the nuclear fibres. 



In the germ cells of spermatozoa in Blatta, the nuclear plate is com- 

 posed of granular thickenings of the nuclear fibres, just as described by 

 Strasburger and Biitschli. A comparison of fresh specimens with those 

 that have been treated with reagents (chromic acid 0.01%) shows that 

 the poles of the spindles, which are rounded in the fresh condition, be- 

 come more pointed, the nuclear fibres thicker, the whole nucleus nar- 

 rower, and that a clear zone is formed about the nucleus. Because this 

 space is artificially produced it cannot be considered a remnant of the 

 old mother nucleus (Eberth), in which the fibrous mass is differentiated 

 as a new nucleus. While the elements of the nuclear plates fuse at the 



* See also Mayzel '76, '76«-^. 



t Compare Strasburger ('77, Taf. XXXIII. Figs. 56-61), where figures of Mayzel's 

 preparations are given. 



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