348 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Fertilization of Elasmobranchs.* — Herr J. Biickert has made some 
observations on the process of fertilization in Pristiurus and Torpedo. 
The merocytes or daughter-nuclei present in the young cleavage-stages 
of Selachians are not derived from the cleavage-nuclei, but are present 
before the copulation of the pronuclei. They are at that time exactly 
like the male pronucleus, and from what the author has been able to see 
in two cases he is led to believe that they have a similar origin to that 
body. If this be so, we may conclude that in Selachians there is a 
physiological polyspermy, and that a number of merocyte-nuclei are 
formed from the spermatozoic heads that make their way into the ger- 
minal discs as well as the male pronucleus. 
B. Histology. 
Cell-division.t — Prof. W. Flemming gave at the meeting of the 
German Anatomical Society an account of the most important advances 
in the cell-theory since 1887. Attention was particularly directed to 
the discovery by E. van Beneden of attraction spheres and central 
bodies. The e.~sence of van Beneden’s doctrine is that there is in the 
cell, in addition to the nucleus, a permanent organ of a special kind — 
the attraction sphere with the central body ; this organ reproduces itself 
by division, if the cell does. The division of the central body precedes 
that of the cell. 1 he rays of the sphere are contractile fibrils which 
attach themselves to the chromosomes, and draw their halves towards 
the poles. They thereby obtain a hold, for the polar bodies are con- 
nected, by the fibrils of the polar radiations, with the general contractile 
cell-structure. An important part, therefore, of the phenomena of 
mitosis has its cause not within but outside of the nucleus. Van Beneden 
supposed that the spheres and central bodies were quite generally 
distributed in all kinds of cells ; not only have they been found when 
mitotic division has been going on, but Flemming has lately discovered 
them in resting cells. In this important address the relations of the 
central bodies to secondary and daughter nuclei are also considered, as 
are also the mechanics of mitotic and amitotic cell and nuclear division. 
The Attractive Sphere.^ — Prof. E. van Beneden has a report on a 
memoir of Dr. 0. Van der Stricht.§ He reminds the reader that, in 
1887, he discovered in the fertilized ovum and the blastomeres of Ascaris 
megaloeephala, a permanent cellular organ which lay beside the nucleus. 
The middle of this “ attractive sphere ” is occupied by a “ cytocentre,” 
around which a medullary and a cortical zone, concentric to the central 
corpuscle, may be distinguished. This sphere undergoes modifications 
like those seen in the cell in repose or during kinesis, but it never dis- 
appears ; it divides before the nucleus, after the division of its cytocentre. 
An important part of the achromatic elements, of which the mitotic 
figures are composed, arise from the attractive spheres. The achromatic 
spindle w*as shown not to have a real existence, but that w'hich does exist 
is tv pair of fibrillar cones; the constituent fibres are clearly endowed 
with contractility, like muscular fibres, and the whole of the achromatic 
* Verbandl. Anat. Gea. 5 en Versamml. (1891) pp. 253-4. 
t Tom. cit., pp 125-44. 
X Bull. Acau. Roy. <le Belgique, lxii. (1892) pp. 77-82, 
§ Tom. cit., pp. 167-92 (1 pi.). 
