424 NOTES. 



the effects of light on the animal organism. Some are of too special a 

 nature and too exclusively addressed to medical physiology — as, for 

 instance, the observation that frogs disengage more carbonic acid in a 

 green light than in a red one ; those on the dependence of the colour 

 of the skin on certain constitutional diseases, &c., while some are not 

 sufficiently detailed to allow of their being used here. To these belongs, 

 for instance, Strethill Wright's observation that polyps pf the higher 

 Acalephse are said to multiply abundantly in the dark by buds, while in 

 the light, and with insufficient supplies of food, they bring forth Medusse. 

 To these also belongs all that has been said of the dependence of lighter 

 or darker tones of colour on the various intensity of light. Thury s obser- 

 vation that, under a green Ught, tadpoles retain their gill-respiration, 

 while their legs are not formed, and that finally they die, comes under 

 the same category. Likewise the phenomena of melanism and hyper- 

 chronism (see Eidgway, ' On the Eelation between Colour and Geogra- 

 phical Distribution in Birds ; ' Silliinaa'e Ajiner. Jmivn., sor. 3, vol. iv., 

 1872, p. 454), which are attributed sometimes to the influence of heat 

 or of light, and sometimes to the general climate. The statement, too, 

 that white rabbits are most easily and certainly reared in a white re- 

 flected light,, is worthy of attention. I owe this remark to Dr. Braun of 

 Wurzburg, who met with it recently in an agricultural journal. In this 

 case, as in all cases of experiment, it is requisite to distinguish between 

 the different causes, and to investigate separately the efiects of each. 

 Hitherto we, the zoologists, have made very light of these physiological 

 labours. Hartmann, and a certain Herr Hesse, declare that a combina- 

 tion of absence of sunlight, cold, and damp, is the cause of the occiir- 

 rence of albinos (I) among snails ; if it is not the one it may be the 

 other. 



CHAPTER IV. 



A^ote 31, jtagie 104. The method of meteorological diagrams could 

 at most be applicable to oases uninfluenced by annual and diurnal 

 variatiphs of temperature ; as those of creatures living in the depths of 

 the sea or of fresh-water lakes, in deep springs, or in the intestines of 

 warm-blooded animals. And even in these cases such curves would be 

 of no practical application, since we cannot transfer them from the 

 animals for which they hold good at the present time, so as to draw 

 any conclusion with regard to unknown, i.e. fossil forms ; nor can we form 

 any opinion as to how the creatures living under such equable tem- 

 peratures would behave if they were suddenly or gradually exposed to 

 the effects of a different degree of heat. In' point of fact, the applica- 

 tion of cHmatio curves — even in its more limited form — has only hin- 



