234 RECORD OF CURRENT RESEARCHES RELATING TO 



the case of Anomala vitis, less than four-millionths of a gramme. 

 Copper was also detected amongst other Coleoptera (notably the larva 

 of Gryllotalpa), and amongst Diptera (Musca domestica), Lepidoptera, 

 Hymenoptera, &c. 



Giunti next sought to ascertain whether other insectivorous 

 animals besides the bat are wont to assimilate the copper present in 

 their insect prey. This was found to be the case with all members 

 of this class subjected to examination, such as snakes, lizards, hedge- 

 hogs, &c. The ashes of the latter contain from one to two ten- 

 thousandths of copper, while the ashes of lizards contain over fifteen 

 thousandths. In their case most of the copper is to be found in the 

 skin of the animal. 



The experiments were likewise extended amongst the Inverte- 

 brates. Various varieties of spiders ; of myriapods, such as lulus 

 terrcstris ; of isopods, such as Armadillidium vulgare ; and of snails, 

 have all given affirmative responses to his tests. Amongst these lulus 

 terrestris contains the largest amount of copper, its ashes showing a 

 percentage of • 18. 



B. INVERTEBBATA. 



Comparative Value of Monochromatic Impressions in Inverte- 

 brates.* — The influence of the different rays of the spectrum on the 

 eyes of the principal types of animals has a special interest in com- 

 parative physiology ; but only recently has it made sufficient progress 

 to admit of experimental research. M. Chatin points out that there 

 are two principal means of investigation. The first originates in 

 the discoveries of Boll, who showed that the retina of many animals 

 contains a so-called visual purple which is effaced in light and gives 

 place to fresh tints whose gradation often indicates the relative 

 lengths of the incident waves. Unfortunately these facts are by no 

 means capable of general application, the substance being wanting in 

 some groups. 



The second and more practical method is that of Dewar, who has 

 shown that the impact of light on the retina gives rise to a special 

 current which disappears directly the visual organ ceases to be in the 

 circuit. " Dewar's Current " thus constituting a criterion of the 

 retinal agitation, it is easy to estimate its intensity by the measure 

 of its dynamic manifestation, the expression of which remains 

 identical in the most varied types of animals. 



In the Arthropoda, and especially in the Decapodous Crustacea 

 and some insects (locusts, &c.), the current asserts itself with absolute 

 constancy, and nowhere are the effects of luminous action more easy 

 to observe, which is explained by the essentially bacillar structure of 

 the eye of these animals. Certain differences in the intensity of the 

 current may be observed to be produced by the different rays, and it 

 is in the yellow-green region that the maximum is reached. 



This tendency is still more marked in the Mollusca, and 

 especially in the Pulmoniferous Gasteropoda : in the yellow rays the 

 current acfiuires its greatest intensity ; it gradually becomes weaker 



* 'Comptcs Kcndus,' xc. (1S80) p. 41. 



