ANIMAL STRUCTURE. 525 



available source of instruction. Not until quite recently 

 has comparative anatomy been studied, with the philo- 

 sophic purpose of gathering answers to the more difficult 

 problems of Biology. Hunter was ridiculed by his pro- 

 fessional brethren ; and some of the sons of those laughers 

 are amongst the most studious of his followers. Men like 

 Swammerdam, Burnett, Lyonnet, Trembley, and Spallan- 

 zani, devoted patient days to the minute labour of investi- 

 gating the structure and functions of insects and polypes ; 

 but even these great workers were moved by curiosity 

 rather than by biological philosophy. The marvels of 

 organisation fascinated them. They saw in these marvels 

 new and surprising proofs of creative wisdom, and were 

 content with such discoveries. Swammerdam, indeed, 

 declares, * that the organisation of these inferior creatures 

 is more wonderful than that of man,' an exaggeration 

 natural and excusable in one who had given his life to the 

 dissection of what in those days of imperfect classification 

 were called 'insects.' Eay, Paley, and other natural 

 theologians, have also sought for arguments in these 

 marvels. But in none of these writers is there a glim- 

 mering of the conception now familiar to every student of 

 Biology, viz. that in these simpler forms we must seek the 

 materials for a true elucidation of vital phenomena." 



In organised beings, the way in which nature works out 

 her most secret processes is by far too minute for observa- 

 tion by unassisted vision ; even with the aid of the improved 

 microscope, only a small portion has, up to this time, been 

 revealed to us. To point out in detail the discoveries 

 made through the employment of this instrument, as 

 regards physiology, would be to give a history of modern 

 biological science ; for there is no department in this study 

 which is not more or less grounded upon the facts and 

 teachings of the microscope. 



To the casual observer, the brain and nerves appear to 

 be composed of fibres. The microscope, however, reveals 

 to us, as was first pointed out by Ehrenberg, that these 

 supposed fibres do not exist, or rather, that they all consist 

 of numerous tubes, the walls of which are distinct, and 

 contain a fluid which may be seen to flow from their broken 

 extremities on pressure. In looking at a muscle, it appears 



