ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 183 



is untenable, at least in the frog ; (2) that the nucleus plays an 

 essential part in pigment formation by some activity which greatly 

 resembles an oxidizing action ; (o) that melanin is formed in the 

 cytoplasm of the cell at the point of known greatest elficiency of the 

 nucleus as an oxidizing agent. More generally, in the cells of embryo 

 frogs, melanin is formed from some substance (probably tyrosin or its 

 derivatives) in solution in the cytoplasm when acted upon by the 

 nucleus (perhaps an oxidase reaction). 



Permeability of Cells for Acids.* — E. Newton Harvey has used 

 a pigment, " antedonin," which occurs in the epithelium of the viscera 

 of a Holothurian, Stichopus ananas, as an indicator for the penetration of 

 acids into cells. Living tissues are resistant to the penetration of all 

 acids except salicylic, benzoic, and possibly valeric. The degree of re- 

 sistance varies with the acid. The penetration rate of HCl is roughly 

 proportional to the concentration. Dead tissues are readily permeable 

 for all acids. There is no relation between the degree of dissociation of 

 the acid and its rate of penetration, or between degree of association and 

 toxicity. There is a general relation between penetrability and lipoid 

 solubility and capillary activity, but it is not exact nor quantitative. The 

 best relation is between penetrability and toxicity. The acids which 

 penetrate most readily are most toxic, irrespective of their strength. 

 Cells behave towards acids and alkalies as if they were droplets of a fat 

 or fat solvent. This suggests that cells must be composed largely of 

 fat-protein combinations, in which the visible physical characteristics of 

 fat are masked. 



Structure and Polarity of Electric Motor Nerve-cell in Torpedo. f 

 Ulric Dahlgren finds evidence that the plasmosome is the heaviest 

 body in the nucleus, undoubtedly heavier in actual weight than the 

 chromatin bodies, and probably of greater specific weight than any of 

 the other nuclear organs, with the probable exception of the karyo- 

 somes. In the young fish the plasmosome seems to have a central or 

 general distribution ; in older or larger fishes it tends to be ventral. 

 This is probably due to its increasing size and weight, together with a 

 lessened resistance on the part of the nuclear-content to slow movement 

 through the mass. Such movement of the plasmosome must depend 

 largely upon growth changes and readjustment in the nucleus, which 

 favour its passage through the achromatin. While very strong electric 

 currents seemed to move the plastosome, weak currents did not influence 

 it. Gravity seems to be the cause of the orientation of the plastosome. 



Trophospong'ia of Spinal Ganglion Cells. | — Emil Holmgren 

 defends his conception of an internal granular-protoplasmic network 

 within the ganglion cells. It sometimes reaches the surface of the cell, 

 and may be connected with cellular elements outside^namely, with pro- 

 cesses of the mantle-cells. Holmgren has made fresh observations on 



* Papers Dept. Mar. Biol., Carnegie Inst. Washington, viii. (1915) pp. 145-56. 

 t Papers Dept. Mar. Biol., Carnegie Inst. Washington, viii. (1915) pp. 213-56 

 (6 pis. and 6 figs.). 



X Arkiv Zool., ix. (1915) No. 15, pp. 1-26 (2pl8. and 2 figs.). 



2 



