580 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
investigated have a framework of fine fibres ; these are uniformly thick, 
optically distinguishable from the matrix, and have a coiled course ; they 
form a mesh work but are not connected at their intersections. The 
fibres arc seen to be movable (in the cilia of Trichoplax ), and they may 
assume a straight course (in cilia and in division). Nucleus and proto- 
plasm have a similar framework, the connectedness of which is not 
hindered by the nuclear membrane. The membranes of nuclei, vacuoles, 
and many cells arise from the coalescence of parts of the fibres. The 
chromatin-masses and nucleoli observed consisted of chromatin-granules 
fused in the meshes of the framework and around the fibres. A nucleolus 
is characterized by the presence of a membrane formed from the frame- 
work, the stainable granules are incapable of movement, but are displaced 
by the movement of the framework. “ Chromatophores ” arise from the 
attachment of chromatin-granules to a support formed from coalesced 
fibres. The attraction-sphere is at first an arbitrary, subsequently a 
spherical portion of the cell, in which the fibres are fixed by a homo- 
geneous connecting mass. The “ polar sun ” and spindle arise from an 
extension of numerous fibres proceeding from the sphere ; the extension 
is perhaps associated with the division of the sphere and the transport of 
its halves to the poles of the spindle, as also with the formation of 
“ chromatophores.” Neither attraction-sphere nor “ polar sun ” are essen- 
tially characteristic of division, nor is a homogeneous circular space 
untraversed by fibres a constant characteristic of the attraction-sphere. 
The spindle-fibres which unite sphere and “ chromatophores ” secure by 
their contraction the division of the latter. In the segmentation-spindle 
of Ascaris megalocephala the mass connecting the fibres in the spheres 
arises from the conical body of the spermatozoon. In the growing zone 
of the ovarian and testicular tubes of Ascaris megalocephala univalens, 
the diffuse chromatin material is collected into a more or less defined 
clump, which, by division into four, forms the chromatin elements of 
four spermatozoa, or the single element of the ripe ovum and three 
polar bodies. Finally, Herr Schneider seeks to explain the import of 
the nuclear membrane in keeping the chromatin together, and the 
numerical constancy of the “ chromatophores ” in the reproductive cells. 
Pigment-cells.* — Dr. B. Solger finds in the dermic pigment-cells of 
the pike’s head most admirable illustrations of attraction-spheres. They 
are very well seen in the pigment-cells of the frontal and ethmoidal 
regions ; in the supra-orbital region, however, the individual cells are 
not readily defined. Sometimes there were several nuclei, but never 
more than one attraction-sphere in the cells ; and Solger thinks that the 
presence of several nuclei without hint of more than one attraction- 
sphere must imply that amitotic nuclear division occurs. 
Minute Structure of Spermatozoa of Mammalia.f — Dr. E. Ballo- 
witz has continued his researches on the minute structure of the sperma- 
tozoa of Mammals. About a score of species have been studied, several 
Bats having first been examined. He finds confirmation of the view that 
the axial filament consists of two apposed bundles of the finest elementary 
fibrils held together by a connecting substance; these fibrils which, 
♦ Anat. Anzeig., vi. (1891) pp. 162-5 (2 figs.). 
t Zeitsclir. f. Wiss. Zool., lii. (1891) pp. 217-93 (3 pis.). 
