EARLY EEVELATIONS OF THE MICROSCOPE. 37 



trusted less to the compound microscope, than to single lenses 

 of high power, the use of which is attended with difficulty, but 

 which are comparatively free from the errors inseparable from 

 the first-named instrument in its original form. The names of 

 Grew and Malpighi, also, appear as frequent contributors to the 

 early volumes of the Philosophical Transactions ; the researches 

 of the former having been chiefly directed to the minute struc- 

 ture of Plants, and those of the latter to that of Animals. Both 

 were attended with great success. The former laid the founda- 

 tion of our anatomical knowledge of the Vegetable tissues, and 

 described their disposition in the roots and stems of a great 

 variety of plants and trees ; besides making out many important 

 facts in regard to their physiological actions. The latter did the 

 same for the Animal body ; and seems to have been the first to 

 witness the marvellous spectacle of the movement of Blood in 

 the capillary vessels of the Frog's foot, — thus verifying by ocular 

 demonstration that doctrine of the passage of blood from the 

 smallest arteries to the smallest veins, which had been pro- 

 pounded as a rational probability by the sagacious Harvey. 



Glimpses of the invisible world of Animalcular life were oc- 

 casionally revealed to the earlier Microscopists, by which their 

 curiosity must have been strongly excited ; yet they do not ap- 

 pear to have entered on this class of investigations, with any 

 large portion of that persevering zeal which they devoted to 

 the analysis of the higher forms of organic structure. Its won- 

 ders, however, were gradually unfolded ; so that in the various 

 treatises on the Microscope published during the eighteenth 

 century, an account of the plants and animals (but especially ot 

 the latter) too minute to be seen by the unaided eye, occupies a 

 conspicuous place. It was towards the middle of that period, 

 that M. Trembley of Geneva first gave to the world his researches 

 on the "Fresh-water Polype " or Hydra; the publication of which 

 maybe considered to have marked a most important epoch in the 

 history of microscopic inquiry. For it presented to the natu- 

 ralist the first known example of a class of animals (of which the 

 more delicate and flexible Zoophytes are, so to speak, the ske- 

 letons) whose claim to that designation had been previously 

 doubted or even denied, the terms "sea-mosses," " seaferns," &c., 

 having been applied to them, not merely as appropriately indicat- 

 ing their form and aspect, but as expressive of what even the most 

 eminent Zoologists, as well as Botanists, considered to be their 

 vegetable nature. And it presented to the Physiologist an en- 

 tirely new type of animal life; the wonderful nature of which 

 was fitted not only to excite the liveliest interest, but also to 

 effect a vast extension in the range of the ideas entertained up to 

 that time regarding its nature and capacities. For what animal 

 previously known, could propagate itself by buds like a plant, — 

 could produce afresh any part that might be cut away, — could 

 form any number of new heads by the completion of the halve* 



