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SUMMARY OF CURRENT RESEARCHES RELATING TO 
are not quadripartite, only bipartite ; and, like the rings and ellipses, 
they are merely transitional forms. The single chromosome formed by 
the fusion undergoes in the equatorial crown a segmentation transverse 
to the axis of its figure, probably the completion of the longitudinal 
splitting of the primary nuclear segment. 
Between the division of spermatocytes I. and spermatocytes II. there 
is a phase of partial rest, but the chromosomes retain their independence. 
The division of spermatocytes II. is especially distinguished by the 
structure and mode of dislocation of the equatorial crown. This crown 
is composed of 24 recurved rods, the chromosomes of the last division, 
which have undergone no longitudinal splitting during the prophases. 
These rods are placed in the crown with their axes parallel to the axis 
of the spindle, and in this position they undergo a transverse segmenta- 
tion. The resulting halves are distributed to the two poles. In this 
case the division is a qualitative and quantitative reducing division in 
Weismann’s sense, but the reduction is not numerical. Indeed, there is 
no numerical reduction of chromosomes in the spermatogenesis of the 
snail. 
The karyokinetic spindle contains a homogeneous axial portion, not 
differentiated into filaments, and bearing no chromosomes. It has 
perhaps some relation to the central spindle of Hermann. It arises, not 
from the cytoplasm, but from the nucleus, and seems to be formed anew 
at the beginning of each kinesis. 
Both nucleus and cytoplasm contain a variable number of “ sidero- 
philous corpuscles,” which appear to be produced by the nucleus, and to 
be expelled therefrom during the resting period, and before kinesis. 
These represent the centrosomes of other authors, but they do not form 
centres or play any mechanical part either in kinesis or in the cell- 
economy at any time. Both karyoplasm and cytoplasm have a reticular 
structure, but there are no “ organic rays ” nor “ attraction-spheres.” 
Mesoderm of Physa fontinalis.* — Herr A. Wierzejski finds that the 
mesoderm in this Gasteropod arises from two sources, from a primitive 
mesoderm-cell and from two ectoderm-cells. The former gives rise to 
the posterior, the latter to the anterior portion of the mesoderm streak. 
The primitive mesoderm-cell contains, even at the 24-cell stage, elements 
of the endoderm ; at the 32-cell stage it produces a small endoderm-cell, 
and becomes for the first time exclusively mesodermic. The two ecto- 
dermic cells referred to become mesoderm-cells only after the end of 
segmentation. Wierzejski briefly compares these results with those 
reached in regard to other Gasteropods, and is forced to conclude that the 
mesoderm of Physa fontinalis is only in part homologous to that of many 
others. 
Terrestrial and Freshwater Molluscs of Kameroon.f — Adolf 
ID’Ailly describes a collection of 100 species, chiefly Gasteropods, from 
Kameroon. Of these no fewer than 35 are new, and the author notes 
that almost the only memoir dealing with Kameroon Molluscs is one by 
E. von Martens in 1876. In describing the collection the author has 
* Biol. Centralbl., xvii. (1897) pp. 388-94. 
t Bihaug K. Svenska Yetensk. Alcad. Handliugor, xxii. (1897) No. 2, 137 pp. 
and 5 pis. 
