164 Tue MIcRoscoPe. 
diameter of one such hair. If then we suppose such an hair to 
be of a round form, it follows that ten thousand of the threads 
spun by the full grown spider when taken together, will not be 
equal in substance to the size of a single hair. 
To this if we add that four hundred young spiders at the 
time when they begin to spin their webs, are not larger than a 
full grown one, and that each of these minute spiders possesses 
the same organs as the larger ones, it follows, that the exceed- 
ingly small threads spun by these little creatures, must be still 
four hundred times slenderer, and consequently that four mil- 
lions of these minute spiders’ threads cannot equal in substance 
the size of a single hair. And if we farther consider of how 
many filaments or parts each of these threads consists, to com- 
pose the size we have been computing, we are compelled to ery 
out, O what incredible minuteness is here! and how little do we 
know of the works of nature! — Written by Leuwwenhek in 1685. 
PROFESSOR VIRCHOW ON PATHOLOGY AND DAR- 
“WINISM. 
In an article contributed to the current number of his 
Archiv. Professor Virchow replies to some views enunciated at 
the Strassburg conference of German naturalists and physicians 
by Dr. Weismann upon Darwinism and Pathology. The ques- 
tion gains interest from the facts adduced by Mr. Sutton in the 
first of his recent lectures before the College of Surgeons, for 
Professor Virchow’s contention is the same as that of Mr. Sut- 
ton—viz., that variations from the animal type are largely 
brought about by deviations in structure strictly speaking path- 
ological. Dr. Weismann, on the other hand, contended that 
such variations are the result of the law of adaptation, and it is 
the position which Virchow contests. He points out that Dar- 
win himself, although not a pathologist, recognized the want of 
a clear line of distinction between monstrosities and mere vari- 
ations. Weismann, however, went so far as to deny the inher- 
itance of acquired properties; but it is difficult to see how 
otherwise one is to express the changes induced by adaptation 
to the environment. The facts of acclimatization are, as Vir- 
chow points out, instances of adaptation, and colonies could not 
be founded if it did not happen that the powers so acquired 
