ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 171 



retina and the pigment epithelium. The fish begins by becoming 

 darker, the melanoblasts spreading out their ramifications and covering 

 the subjacent layer of crystals which produce the golden shimmer. After 

 more than two*^ years the fish re-acquires the golden shimmer, the 

 phagocytes gradually devouring the black chromatophores, and re- 

 exposing the subjacent layer. 



The ovaries become smaller and more compact. The ova coalesce 

 in clumps, and a peculiar process of atrophy sets in. The structure of 

 the pigment-epithelium of the eye completely changes, there being a 

 complete disappearance of the thin cell-processes which extend normally 

 between the rods and cones. All the cells become smaller. The layer 

 of rods and cones disappears entirely from the retina, and the same is 

 true of the external nuclei. There is also a complete disappearance of 

 the layers of nerve-cells and nerve-fibres and of the membrana limitans 

 interna, i.e. the terminal portions of Miiller's fibres. In short, there is a 

 profound atrophy, and the fish becomes blind. As the author points out, 

 the same might happen in an individual cave-fish. 



b. Histology. 



Phenomena of Secretion in Mammary Gland.* — H. Hoven has 



studied this in guinea-pigs. At the beginning of secretion the cyto- 

 plasm of the cells contains numerous chroudriosomes, in the form of long 

 undulating filaments. These break up iato granulations, some of which 

 are transformed into secretory granules (probably becoming casein and 

 sugar), while others are transformed into minute drops of fat, which 

 may coalesce into larger drops. 



Structure of Nerve-cells at Different Ages.j — M. Miihlmann has 

 studied the changes that occur during the growth of nerve-cells. His 

 subjects have been man, ox, sheep, rabbit, and guinea-pig. The proto- 

 plasm is early distinguished from that of other tissues by containing a 

 basichromatin substance. This is not essentially different from that of 

 nuclear material. It occurs, to begin with, in diffuse granules. These 

 collect in interfascicular groups, and form the tigroid substance. This is 

 probably in solution in life, and becomes granular in death. When it is 

 well-developed, iiTegular fatty granules appear in the protoplasm. In 

 the course of gro'oth these increase and become pigmented, and form 

 large aggregates in the adult. In advanced age the lipoid character 

 disappears, and the pigment character is left. 



In the nucleus there is at first an abundant nuclein-content. This is 

 gradually reduced. It passes from several nucleoli to one, becomes an 

 envelope around this, is dissolved into it, and finally disappears from the 

 nuclear region. In the nucleolus lipoid bodies are formed, like those in 

 the cytoplasm. But they do not accumulate. They pass away at an early 

 age and leave vacuoles. 



•'to'- 



Structure and Function of Lamellar-corpuscles.| — S. von Schu- 

 macher has studied these in the mesentery of the cat, in the region of 



♦ Anat. Anzeig., xxxix. (1911) pp. 321-6 (4 figs.). 



t Arch. Mikr. Anat., Ixxvii. (1911) pp. 194-231 (1 pi.). 



i Arch. Mikr. Anat., Ixxvii. (1911) pp. 157-93 (1 pi. and 4 figs.). 



