614 SUMMARY OF CURRENT RESEARCHES RELATING TO 
Origin of the Centrosoma.* — Dr. A. Brauer records some observa- 
tions made on the spermatocyte of Ascaris megalocephala var. univalens , 
which he regards as conclusive. In the nucleus of the spermatocyte at 
the stage when a four-partite chromosome was present, he saw, apart from 
the nucleolus, a relatively large rounded body. During the formation 
of the first spindle, threads radiate out from this body, in all directions, 
to the chromosome ; it then lengthens and divides. The halves then 
separate, while the threads communicating with the chromosome remain 
unbroken ; as they separate, the nucleus becomes lengthened in the same 
direction. At last, at two opposite points the two bodies pass through 
gaps in the nuclear membrane into the cell-protoplasm. Here a radiating 
arrangement of cell-protoplasm becomes obvious round each. The two 
structures thus formed from the original spherical body are undoubtedly 
the centrosomes. In some cases before its division the centrosome 
leaves the nucleus and appears on the outside of its membrane. In this 
observed case it is clear that the centrosome belongs to the nucleus 
and not to the cell-protoplasm. The strongly accentuated distinction 
between nucleus and centrosome thus breaks down, and increased proba- 
bility is given to the view which regards the chromatin elements as the 
bearers of hereditary tendencies, the centrosome as simply an organ of 
division. The author’s observations also lead him to conclude that the 
whole of the spindle is nuclear in origin. 
Muscle-spmdles.f — Dr. L. Kerschner gives a useful summary of 
investigations (since 1888) on muscle-spindles. He dismisses various 
interpretations, e. g. that they are pathological growths, or that they are 
merely transitional structures. Most striking is the well-developed 
terminal nerve-apparatus. This cannot be motor, for on each of 
Weismann’s fibres there is at least one motor terminal plate, and there 
is no connection between the terminal apparatus and the motor tracts. 
Kerschner’s own interpretation is that the apparatus is sensory. In 
support of this he marshals various arguments, and promises a fuller 
statement. 
Intercellular Bridges between Smooth Muscle Cells and Epithelial 
Cells.t — Dr. M. Heidenhain finds that in the poison-glands of Triton 
the ensheathing muscle-cells are connected by plasmic bridges with the 
ectodermic epithelial cells at the neck. He regards this connection as 
of primary significance, and as a proof that these muscle-cells of the 
skin-glands belong genetically to the ectoderm. In the case of the pelvic 
and cloacal glands he believes that the muscle-cells are in the same 
way demonstrably endodermic. 
y. General. 
Nerve-cord and Notochord in Amphioxus.§ — Herr B. Lwoff dis- 
cusses the import of the supporting fibres associated with the nerve-cord 
of Amphioxus. Those which lie ventrally are the strongest. The 
ependyme cells, homologous with similar elements in other Vertebrates, 
form the original supporting tissue, and remain much more distinct and 
* Biol. Centralbl., xiii. (1893) pp. 285-7. 
t Anat. Anzeig., viii. (1893) pp. 449-58. J Tom. cit., pp. 404-10 (1 fig.). 
§ Zeitschr. f. wiBS. Zool., Ivi. (i893) pp. 298-309 (1 pi.). 
