34 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Structure of Pigment-cells.* — V. Franz has made a study of 

 various types of pigment-cell. The concentration of the pigment 

 depends on intracellular streaming movements of the pigment grannies. 

 The plasmic radial structure of pigment- cells has its basis in an intra- 

 cellular skeleton, somewhat like that of some Acantharia. 



Regeneration of Intestinal Epithelium in Cobitis fossilis.|— 

 Helene Lupu finds that the epithelial cells degenerate by the breaking 

 down of the nuclei and dissolution of the chromatin. The regeneration 

 occurs by superficial mitosis at the expense of persisting embryonic- 

 basal cells. There is no evidence of any passage of connective-tissue 

 elements through the basal membrane. 



Interstitial Tissue of Mammalian Ovary.j — Hans von Winiwarter 

 has studied this in man and other mammals. It probably occurs in all 

 mammals. It appears periodically, as if in instalments, and probably 

 has a trophic role. There is no warrant for speaking of an interstitial 

 gland. 



Regeneration of Peripheral Nerves.§ — Ptoss G-. Harrison cut the 

 nerves of one side of the tail of larva? of Bona sylvatica just beyond 

 the point of emergence from between the myotomes, and observed the 

 prpcess of degeneration and regeneration from day to day. The de- 

 generative processes take place very rapidly. In less than 24 hours the 

 medullary sheath is completely disintegrated beyond the lesion, and for 

 a very shoit distance central to it. In the axis-cylinder of both the 

 medullated and non-medullated nerves, the signs of degeneration 

 are less marked, but unmistakable. The Schwann-cells become less 

 regularly spindle-shaped, with a somewhat humpy surface, and do not 

 adhere so closely to the axis-cylinder. 



After one or two days the cut ends of many of the nerves have 

 united by a protoplasmic bridge. In such cases the degeneration of the 

 peripheral part of the axis-cylinder is immediately arrested, indicating 

 that a primary healing of nerve-fibres is possible. The medullary sheath 

 is not rehabilitated immediately, and the process of re-formation of this 

 structure resembles its initial development. 



When the peripheral portion of a nerve fails to unite with a central 

 stump, degeneration continues till the nerve disappears. AVhen a 

 central stump fails to unite with a peripheral end, regeneration takes 

 place by a comparatively slow process in a centrifugal direction. There 

 is no indication whatever of any power of " auto-regeneration " in the 

 nerves whose connection with the central end remains severed. 



c. General. 



Habits of Sloths. || — A. Menegaux points out that sloths (Bradypus) 

 are not exclusively arboreal — that they sometimes descend to the 

 ground and seek out another tree. They descend backwards. They 



* Biol. Centralbl., xxviii. .(1908) pp. 545-8 (13 figs.). 



t Arch. Zool. Exper., ix. (1908) pp. 417-28 (1 pi.). 



% Anat. Anzeig., xxxiii. (TJ08) pp. 1-9 (5 figs.). 



§ Reprint from Amer. Journ. Anat., vii. (Feb. 29, 1908) 1 p. 



|| Comptes Rendus, cxlvii. (1908) pp. 1079-82. 



