240 SUMMARY OF CURRENT RESEARCHES RELATING TO 



lamprey, and other crawling fishes, the eyelids play no part, but the true 

 cornea is differentiated into three strata : (1) a thick, resistant, immobile 

 superficial stratum, with external epithelium ; (2) a deep, delicate, 

 inner layer, moving with the eye, with internal epithelium ; and (3) a 

 median stratum, formed of lamellae of connective tissue parallel to the 

 surface, and loosely united so as to form a sort of articulating layer. 



J. A. T. 



Rate of Nerve-conduction in Sea-water. — Alfred Goldsborough 

 Mayer (Amer. Journ. Physiol., 1917, 44, 591-5). In sea-water 

 between salinities of 18 to 40 p.c, the rate of nerve-conduction in the 

 jelly-fish Cassiopea varies as a straight line in relation to the electrical 

 conductivity, or the degree of dissociation of the cations Na, K, Mg and 

 Ca surrounding the nerves. Thus, if y be the rate of nerve-conduction, 

 that in normal sea-water of 36-24 p.c. salinity being 100 ; and if x be 

 the relative electrical conductivity of the sea-water, that of normal sea- 

 water of 36*24 p.c. salinity and 8*22 Ph being 100, then 



y = 0-945 a; + 4*4. 



In sea-water of more than 40 p.c. salinity there is 'a decided and 

 constantly augmenting reduction in the rate of nerve-conduction. 



J. A. i. 



Colour-sense in Pishes. — 0. Polimanti {Arch. Ital. Biol., 1915, 

 64, 300-5). The reactions of the fishes studied seem to depend on 

 the depth at which they usually live. It is well known that the rays of 

 long wave length are absorbed not far from the surface, while those of 

 short wave length penetrate further. Polimanti found that violet, blue, 

 and green light had an almost constant influence on the number of 

 respirations in the fishes studied, while red light and diffuse light had a 

 very variable effect. By red and diffuse light the fishes experimented 

 on are rarely affected in normal life. The general conclusion is that the 

 fishes used are like completely colour-blind persons. J. A. T. 



Colour-discrimination in Sticklebacks and Mud-minnows. — 

 Gertrude Marean White {Journ. Expor. Zool., 1919, 27, 443-98, 

 10 figs.). Experiments were made with the American stickleback 

 {Eucalia inconstans) and mud-minnow {Umhra limi) in regard to their 

 powers of association and colour-discrimination. It was found that the 

 mud-minnows could discriminate between many colours, and the stickle- 

 backs to a less degree. Both established associations between food and 

 various colours. Experiments with patterns show that these are not 

 very important in the search for food. The perception of colour and 

 movement seems to be of chief importance. In sticklebacks the sense 

 of smell is also used to some extent. " The behaviour of fishes is stereo- 

 typed. The associations formed are simple, few in number, and not 

 open to ready modification, though they may be fairly permanent, and 

 may involve considerable acuity in sensory discrimination. Learning 

 seems to consist for the most part in the gradual elimination of useless 

 movements and the establishing of those which are useful." There is 

 nothing to indicate ability to recall an image of past experience, but 



