122 On muscular Motion. 



is placed externallv, where the body is reduced below a cer- 

 tain magnitude, or where the movements of the animal are 

 not to be of the floating kind ; in which last case the bulk 

 is not an absolute cause. The examples of testaceous vermes, 

 and coleopterous, as well as most other insects, are univer- 

 sally known. 



The opinion of the muscularity of the crystalline len? of 

 the eye, so ingeniously urt;ed bv a learned member of this 

 society, is probably well founded; as the arrangement of 

 radiating lines of the matter of muscle, from the centre to 

 the circumference of the lens, and these compacted into 

 angular masses, would produce specifjc alterations in its 

 figure. 



This rapid sketch of the history of muscular structure 

 has been obtruded before the Royal Society to introduce the 

 principal experiments and reasonings which are to follow : 

 they are not ordered with so much exactness as becomes a 

 more deliberate essay ; but the intention already stated, and 

 the limits of a lecture, arc offered as the apology. 



Temperature has an essential influence over the actions 

 of muscles : but it is not necessary that the same tempera- 

 "ture should subsist in all muscles during their actions ; nei- 

 ther is it essential that all the nniscular parts of the same 

 animal should be of uniform temperatures for the due per- 

 formance of the motive functions. 



It appears that all the classes of animals are endowed 

 with some power of producing thermoroetrical heat, since 

 it has been so established m the amphibia, pisces, vermes, 

 and insecta, by iVIr. John Hunter; a fact which has been 

 verified to my own experience: the term co/d- Hooded is 

 therefore only relative. The ratio of this po\|ver is not, 

 however, in these examples, sufficient to preserve their 

 equable temperature in cold climates ; so that they yield to 

 the changeti of the atmosphere, or the medium in which 

 they reside, and most of them become torpid, approaching 

 to the degree of freezing water. Even the mammalia and 

 aves possess only a power of resisting certain limited degrees 

 of cold; and their surfaces, as well as their limbs, being 

 distant from the heart and principal blood-vessels, the mus- 

 cular parts so situated arc subject to considerable variations 

 in their temperature, the influence of which is known. 



In those classes of animals which have little power of 

 generating heat, there are remarkable differences in the 

 structure of their lungs, and in the composition of their 

 blood, from the mammalia and aves. 



Respiration is one of the known causes which influences 



the 



