324 THE CANADIAN NATURALIST. [Sept 



altogether, and permanently, unlike the parent. The term 

 Heterogonesis, however, has unfortunately been used in a different 

 sense, and M. Milne-Edwards has therefore substituted for ifc 

 Xencg3nesis, which means the generation of something foreign. 

 After discusing Redi's hypothesis of universal Biogenesis, then, 

 I shall go on to ask how far the growth of science justifies his 

 other hypothesis of Xenogenesis. 



The progress of the hypothesis of Biogenesis was triumphant 

 and unchecked for nearly a century. The application of the 

 microscope to anatomy, in the hands of Crew, Leeuwenhoek, 

 Swammerdam, Lyonet, Valiisnieri, Beaumur, and other 

 illustrious investigators of nature of that day, displayed such a 

 complexity of organization in the lowest and minutest forms, and 

 everywhere revealed such a prodigality of provision for their 

 multiplication by germs of one sort or another, that the hypothesis 

 of Abiogenesis began to appear not only untrue, but absurd; and 

 in the middle of the eighteenth century, when Needham and 

 Buffon took up the question, it was almost universally discredited. 

 (' Nouvelles Observations,' p. 169 and 176.) 



But the skill of the microscope-makers of the eighteenth 



century soon reached its limit. A microscope magnifying 400 



diameters was a chef-d\euvre of the opticians of that day ; and, 



at the same time, by no means trustworthy. But a maguifying- 



power of 400 diameters, even when definition reaches the exquisite 



perfection of our modern achromatic lenses, hardly suffices for 



the mere discernment of the smallest forms of life. A speck^ 



only 2V of an inch in diameter, has, at ten inches from the eye, the 



same apparent size as an object Toornjth of an inch in diameter,, 



when magnified 400 times ; but forms of living matter abound^ 



the diameter of which is not more than Tuoiruth of an inch. A 



filtered infusion of hay allowed to stand for two days, will swarm 



•with living things, among which, any which reaches the 



diameter of a human red blood-corpuscle, or about aVooth of an 



inch, is a giant. It is only by bearing these facts in mind, that 



we can deal fairly wath the remarkable statements and speculations 



put forward by Buffon and Needham in the middle of the 



eighteenth century. 



When a portion of any animal or vegetable body is infused io 



water, it gradually softens and disintegrates ; and as it does so,, 

 the water is found to swarm with minute active creatures, the so- 

 called Infusorial Animalcules, none of which can be seen excepfe 



