6^2 THE POPULAR SCIENCE MONTHLY, 



Fig. 4 represents a front view of Paramecium caudatum. He is 

 not an architect, but a wandering, idle sort of fellow, often seen in 

 company with our more staid and settled house-keepers. He gets into 

 the oddest shapes imaginable. If he is a little cramped for room it 

 does not seem to inconvenience him in the least, for his body is so 

 flexible he can make it fat and dumpy, or long and slender, just as 

 the occasion seems to require. If they have any police regulations in 

 this fairy-world, he must be a great trial to the authorities, eluding 

 their grasp, and bowing to them from some other quarter, entirely 

 transformed. But, when there is nothing to interfere with his loco- 

 motion, he looks very much like a leaf, as is seen in our figure. He is 

 covered all over with rather short, stifl" hairs, or cilia, that look like 

 porcupine-quills — perhaps they are his weapons of defense. He is 

 not carnivorous, but lives on a vegetable diet, and is so transparent 

 that we can always tell what he has taken for his dinner. His favorite 

 food seems to be diatoms. These are beautiful little plants encased 

 in a shell of various forms and colors. This curious animal sometimes 

 manages to swallow two diatoms at once, almost as long as his body, 

 and then he seems rather awkward and stifi", with two great logs on 

 his stomach ! But he manages, somehow, to absorb the nutritious, 

 vegetable part of the diatom, and throws aside the beautiful transpar- 

 ent shell, which he has not broken nor injured at all in the operation. 



mAUGUKAL ADDEESS BEFORE THE BRITISH 

 ASSOCIATION 



Br Prof. JOHN TYNDALL, D. C.L., LL. D., F. JR. S., President. 



AN impulse inherent in primeval man turned his thoughts and 

 questionings betimes toward the sources of natural phenomena. 

 The same impulse, inherited and intensified, is the spur of scientific 

 action to-day. Determined by it, by a process of abstraction from 

 experience we form physical theories which lie beyond the pale of ex- 

 perience, but which satisfy the desire of the mind to see every natural 

 occurrence resting upon a cause. In forming their notions of the ori- 

 gin of things, our earliest historic (and doubtless, we might add, our 

 prehistoric) ancestors pursued, as far as their intelligence permitted, 

 the same course. They also fell back upon experience, but with this 

 difference — that the particular experiences which furnished the weft 

 and woof of their theories were drawn, not from the study of Nature, 

 but from what lay much closer to them, the observation of men. Their 

 theories accordingly took an anthropomorphic form. To supersensual 

 beings, which, " however potent and invisible, were nothing but a 



