ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 349 



epidermis are evoked by thermal, chemical, osmotic or contact stimuli, 

 but strong light has no appreciable influence on the epithelial cells. 

 After contraction the epithelial mass may spread out as widely as before. 



Epidermis from amphibian larva' may be kept alive for several 

 months if it is transferred occasionally into fresh culture medium. 

 Mitotic cell divisions were observed in the living cells fifty days after 

 implantation into the culture medium. Amitotic nuclear divisions 

 were found, especially on preparations that were kept for several weeks 

 without a fresh supply of nutrient fluid. 



Epidermal cells from embryos of Diemyctylus were seen to undergo 

 differentiation in vitro into the different types of cells found in the 

 epidermis of late larval stages. Pieces of epidermis from the adult frog 

 form extensions much like those from the larva, but growth is less 

 rapid. The extensions of the epidermis in both larval and adult forms 

 are due to the amoeboid activity of the hyaline protoplasm along the 

 margin of the extending mass. 



Microscopical and Chemical Study of Feather Pigments in 

 Pigeons.* — Orren Lloyd-Jones has sought by experiment to analyse 

 the factors conditioning the various self -colours of the tumbler pigeon. 

 The pigments concerned belong to the melanin series and are granular 

 in nature. There is a red-brown pigment which produces the red and 

 yellow colours in tumbler pigeons. In red birds this pigment always 

 exists as spherical granules, which are in "typical red" about 0*3 fx in 

 diameter, but in " plum colour " they are 2 ll or more in diameter. In 

 reds there is abundant pigmentation in the intermediate cells of the 

 epidermis, independently of specialized pigment cells. In yellows the 

 pigment is so finely divided that its granule form cannot be determined. 

 There is a black pigment which under different conditions produces the 

 colours black, dun, blue, and silver. In black birds this pigment may 

 exist as spheres • 5 /j. in diameter, or as rods 1 /a long. Some blacks 

 show entirely one category of granule form and some entirely the other. 

 In most blacks, however, both kinds are to be seen, although there is 

 commonly a marked predominance of one or the other type. In blacks 

 the pigment cells are better developed than in reds and elaborate a 

 greater proportion of the pigment. 



Pigment granules in dun birds are invariably spherical in form and 

 about • 3 ij. in diameter. Dun colour may be seen in birds which are 

 not dun genetically, but differences in granule form and distribution 

 show that this is not the character dun which behaves as a unit in 

 inheritance. 



"Blue" of pigeons is produced by the black pigment clumped and 

 distributed in such a way as to produce the blue effect. Granules in 

 blues are spherical, 0-8 /* to 1 /* in diameter. The development of the 

 pigment in blues is not so promiscuous and "disorderly" as in blacks. 

 It is apparently controlled by an influence lacking in blacks. 



After the pigment arrives in the barbules it undergoesa ••clumping" 

 process which gives it its characteristic distribution. The feathers from 



* Journ. Exper. Zool., xviii. (1915) pp. 453-508 (7 pis.). 



