96 ANIMALS KILLED IV; 
recognized when the fand is prefented on a flider 
to the microfcopes Then they are in the figure 
of minute dry globules of a reddifh yellow co- 
jour, which, by humectation, expand into fo many 
animated wheelers. 
Befides roofs and tiles, particular waters con- 
tain them. Both Baker and myfelf have often feen 
them in ditches; and I have taken many from 
pools, marfhes, and even holes of ftanding wa- 
ter. | 
The wheel animals of the earth are, in. my 
opinion, the origin of thofe of roofs: and this 
feems a neceflary conclufion ; at leaft we cannot 
fay thofe of one roof come to another, which 
fuppofes a particular cafe: but to fpeak general- 
ly, and confider the origin of the matter, we 
muft derive their origin elfewhere, confequently 
recur to the waters. The manner in which they 
pafs from the earth to roofs, may be eafily con- 
ceived; in their dry ftate, the wind may tranf- 
port them through the air, whenever their native 
element is entirely or partially dried up. 
In my ftudies on thefe curious beings, I have 
always reflected on a moft important problem, to 
inquire into their mode of propagation. With 
this view, I have ifolated them in watch-glaffes 
like infufion animalcula, putting one in each ; 
but I could never obferve them propagate either 
by fhoots or divifion: though both ways are 
common 
