572 SUMMAltY OF CUIUIENT RESEARCHES RELATING TO 



(^ to J expansion), while the melanophores of seeing larvae that have 

 been kept for some time in darkness (more than five days) are expanded 

 (I to I expansion), thus showing, under long-continued illumination 

 and darkness, what has been called a secondary reaction. 



Chromatophores of Brook Trout.* — John N. Lowe has subjected 

 the chromatophores of SalveUnus fontinalis to various chemical agents. 

 The young stages have only one kind of pigment cell, the melanophore ; 

 from two to fourteen days they do not react to background ; this occurs 

 after the yolk is absorbed. In the presence of oxygen, the pigment cells 

 remain expanded ; when hydrogen is substituted the pigment cells con- 

 tract, and the embryos die. Carbon-dioxide causes contraction. Boiled 

 or distilled water causes contraction. In the potassium salts there is 

 rapid contraction ; in the neutral salts of sodium there is slow contrac- 

 tion. The influence of alcohol, strychnine, morphine, nicotin, and other 

 agents is recorded. 



Scales of Spring Salmon.f — C. McLean Fraser has made a micro- 

 scopic study of the scales of the Pacific salmon, Oncorhynchus tscha- 

 wytscha. The growth of the scale is a reliable indication of the growth 

 of the fish. Annual bands of growth appear on the scale, each consist- 

 ing of a wide portion with tlie lines on it somewhat distant, and a narrow 

 portion with the lines closer togeti\er. The <parrow band may be called 

 the " winter check " appropriately, because, although the retardation of 

 growth is due to lack of food rather than to a lowering of the tempera- 

 ture, it is produced in the winter months, January, February and March, 

 with indications of it in December and April. 



There are two types of scales, since some of the salmon migrate to 

 the sea as fry and have no fresh-water record on their scales, while others 

 migrate as yearlings or fingerlings after having a year of comparatively 

 slow growth in the fresh-waters clearly indicated on their scales. 



The majority of both types mature in their fourth or fifth years. 

 Probably a greater percentage of the "sea-type" than of the "stream- 

 type " mature in the fourth year, but a majority of the whole number 

 are of the " sea-type." The fish that mature in the fourth year are, as 

 a rule, among the larger of the year-class. Probably if enough third- 

 year grilse were examined there would be proof that they are among 

 the largest of the year-class. 



The " sea-type " fish has a decided advantage throughout life, both 

 in length and in weight, so much so that an average fish of the " stream- 

 type," mature in the fifth year, is scarcely larger than a " sea-type " fish 

 mature in the fourth year. If they are both in the same year when 

 mature, either the fourth or fifth, there is an average difference of six 

 or seven pounds. Unless there is some other preponderating reason 

 for keeping spring salmon in rearing ponds for a year, it is decidedly 

 unwise to do so, as, taking it either in size or in time, there must be a 

 difference of at least 20 or 25 p.c. in favour of the "sea-type" fish. 



♦ Journ. Exper. Zool., xxiii. (1917) pp. 147-93 (1 pi. and 3 figs.). 

 t Contributions to Canadian Biology, 1917, pp. 11-32 (15 figs.). 



