of the Powers of producing Heat and Light. 24-3 



which are said to be luminous or phosphorescent^ such as the 

 glow-worm and the fire-fly among insects, and many species 

 of minute Medusa and Crustacea among the inhabitants of the 

 ocean. 



The author deduces from all the facts hitherto promulged 

 on these subjects, the following principal law : viz. That in 

 the animal kingdom the powers of producing (or evolving) heat 

 and lights respectively^ are reciprocally in the inverse ratio of 

 each other. 



Of this law, with reference to its consequences in particular 

 cases, the following statement may be regarded as an expan- 

 sion ; that classification of the animal kingdom being adopted 

 for the purpose, which has been shown, by Mr. William S. 

 Macleay, by a course of strict induction detailed by him in 

 his Horcc Entomologicfjo^ to express the natural affinities of the 

 beings composing it. 



If we represent by a circle, as Mr. Macleay has done*, the 

 series of affinities returning into themselves, which is presented 

 by the beings of the animal kingdom, when we consider the 

 totality of the characters of every species with reference to the 

 totality of those of every other species, and to the aggregate 

 character of each of the more or less comprehensive groups into 

 which they are connected by their mutual affinities, we shall 

 observe, on comparing this mere expression of known affi- 

 nities with the facts relating to the production of heat and 

 light by animals, the following phaenomena. 



In the Mammalia and Birds, forming a certain arc of the 

 circle, animal heat is at its maximum ; while animal light does 

 not sensibly exist, and if it exist at all is at its minimum. 



In certain Crustacea, Radiata, Acrita, and Tunicataf, 

 forming an opposite arc of the circle, animal light is at its 

 maximum, while animal heat does not sensibly exists and if 

 it exist at all is at its minimum. 



* HorcB Entomologic<s, p. 318. In order that the members of the Sec- 

 tion of the British Association before whom this paper was read might 

 be enabled readily to trace the distribution of animal heat and light here 

 announced, a large diagram was exhibited to them, which was an exact 

 transcript of that given by Mr. Macleay, loc. cit. 



t The phaenomena of natural distribution discovered by Mr. Macleay, 

 and the arrangement of the animal kingdom which is the expression of 

 those phaenomena, being even yet far less known to the scientific world 

 than their importance demands, his nomenclature, though differing very 

 little from that of contemporary naturalists, (having been, in fact, for the 

 most part selected from their works,) may not be immediately understood, 

 especially as it contains some peculiar applications ; a few synonyms of 

 the groups mentioned in this paper are therefore subjoined. 



The groups denominated Vertebrata, Mammalia, Birds, and Fishes, require 



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