Recent Researches on the Infusoria. ^93 



ascrib^^th'e'bVfgm'of infusoria to ova conveyed hfih^ air; an 

 assumption which the supporters of the doctrine regard as 

 highly improbable, and which, if admitted as true, they con- 

 sider inadequate to explain the production of infusoria in all 

 the conditions under which it is reported to have taken place by 

 observers worthy of credit. It is true, that Dr Ehrenberg never 

 witnessed the spontaneous origin of infusoria ; but before deny- 

 ing the possibility of its occurrence, and discarding the theory 

 of spontaneous generation, as unnecessary to account for the 

 facts, it was incumbent on him to have subjected anew to a ri- 

 gid examination the observations of those .who have arrived at 

 an opposite conclusion from himself, and either exposed the fal- 

 lacy of their experiments, or shown how they were to be ex- 

 plained on a different view from that adopted by their authors. 

 It is the more to be regretted that he has not favoured us with 

 such a critical examination, as, from his extensive knowledge of 

 the different species of the animals in question, his intimate 

 acquaintance with their mode of life, and his superior methods 

 of observation, he is singularly well fitted for the task. 



II. On the Eyes of the Infusoria. 



Many of the infusoria have one or more coloured spots on 

 the surface of their bodies, which Dr Ehrenberg regards as their 

 eyes. These spots, which are mostly of a red colour, were no- 

 ticed in a few of the infusoria by preceding observers, by some 

 of whom they were even designated by the name of eyes ; but 

 it seems probable that that term was used merely by way of 

 comparison, and was not intended to imply that such spots 

 were really the eyes or organs of vision of the animals in which 

 they were observed. Professor Njtsch of Halle, however, who 

 had discovered them in some species of Cercaria, endeavoured 

 to prove that they were eyes in a real sense ; and he has there- 

 fore the merit of first pointing out in a distinct arid explicit 

 manner the existence of such organs in the infusoria. Dr Eh- 

 renberg, in his former memoirs, described the eyes in several of 

 the Rotatoria. He has since found them in two-thirds of the 

 known genera belonging to that class, and in all the species of 

 these genera without exception ; and what is more remarkable, 

 Ke has discovered them in many <if the smaller aiid less perfect 



