290 Account of Professor Ehrenberg^s 



great argument adduced in its favour, tliat which was drawn 

 from the supposed identity of the simplest infusoria with mere 

 organic molecules, since these infusoria have been shown to pos- 

 sess a much more complex structure than had previously been 

 imagined, differing only in degree from that of the more perfect 

 animals, and totally inconsistent with the notion of their identi- 

 ty with simple organic molecules, an opinion founded on imper- 

 fect and erroneous observation. 



The method of observation adopted by Professor Ehrenberg, 

 in conducting the present part of his inquiry, was the follow- 

 ing. He poured into a watch-glass a small quantity of water 

 containing some of the larger kinds of infusoria, which, by a 

 little practice, may be perceived with the naked eye. Of these 

 he took out a single one with the end of a feather, cut into a 

 convenient shape, and placed it under the microscope, in order 

 to ascertain whether it contained perfect eggs, and, if any were 

 present, to note their number. This being done, he put the 

 animal into a narrow glass-tube, closed at one end like a small 

 test-tube, and tilled with water, in which he had previously sa- 

 tisfied himself, by careful examination with the microscope, that 

 no similar animals were present. A blade of the lemna was 

 laid on the top of the water, to preserve it from dust, and pre- 

 vent it from becoming putrid by stagnation. By this contrivance 

 he was enabled to carry on his observations on several separate 

 individuals at the same time. 



He first made choice of the Hydatina senta, which he selected 

 as an example of the infusory animalcules belonging to the class 

 of Rotatoria ; this animal being about one-sixth of a line in 

 length, and therefore well fitted for examination. In the month 

 of November 1830, twelve different individuals of the Hydatina 

 senta were subjected to observation in the manner described, 

 and the following were the results : 



1. One individual survived eighteen days. As it was full 

 grown when put into the tube, and then probably two or three 

 days old, and as it did not die a natural death, but was destroyed 

 by accident, the duration of life in this individual may, with 

 great probability, be estimated at more than twenty days. 



% The hydatina is propagated by eggs : they were observed 

 first within the body of the parent animal ; then deposited in 



