312 BULLETIN OF THE 



Their great number and enormous size as compared with that of the 

 cell, their nearness to the surface, and their diffuse arrangement, com- 

 bine to make this an interesting case of nuclear reconstruction. 



Ed. van Beneden (76'^, pp. 38, 47-52) discovered in one of the two 

 forms of the parasitic Dicyema certain spherical striate bodies. These 

 were always found in the vicinity of the germarium (germigene), and in 

 size were, when occurring singly, like the germs. These were for a time 

 thought to be spermatophores, but the author's attention was at length 

 directed to their similarity to the nuclei of dividing cells as described 

 by BUtschli and Strasburger. They were ultimately found to be germ 

 cells in process of division. Immediately before dividing, says Van Be- 

 neden, the germ (a single cell) becomes very granular and opaque ; the 

 nucleus increases considerably in size, its contents lose much of their 

 transparency, and its nucleolus disappears; then an extremely clear, 

 meridional striation is developed at the surface of the nucleus ; the striae 

 are not the result of an alignment of corpuscles or granules, but are due to 

 the presence of continuous, homogeneous fibrils, formed of a very refrin- 

 gent substance. If one of its poles is directed toward the observer, this 

 striation appears radial. The volume of the nucleus increases at the 

 expense of the surrounding protoplasm to such an extent that the latter 

 is reduced to a thin layer of granular substance enveloping the former. 

 There soon appears at each pole of the nucleus a refringent "corpuscle 

 polaire," around which are grouped very fine granules. The two poles 

 become diff'erentiated into granular polar disks, in which the ends of the 

 meridional fibres are lost. At this time a polar view shows that the 

 radial striae are somewhat curved (PI. I. Fig. 28, PL III. Fig. 3), — much 

 as the vitelline rays are in Limax (Fig. 56), — proof that the fibres do 

 not exactly follow the direction of meridional lines, but are a little 

 oblique. The fibres exist only at the surface of the nucleus. The polar 

 disks become thicker, more refringent, and distinct ; the fibrils less clear, 

 as if their substance were attracted toward the poles. The author has 

 but rarely met with fibrils a little thicker in the middle than elsewhere ; 

 aside from this, he has seen no indication of either equatorial or lateral 

 nuclear plates. Later, the polar disks are in some way condensed into 

 small, discoidal, refringent bodies (pronucleus derive), around each of 

 which is accumulated in the protoplasmic body a clear substance from 

 which radial [extra-nuclear] striae are sometimes seen to diverge (pronu- 

 cleus engendre). The Zellplatte of Strasburger appears in the equator 

 as a dark granular plate ; a circular furrow appears at the equator of 

 the cell ; the cell-plate divides into two ; the two hemispherical cells 



