REPORT ON AXIMA-L PHYSIOiOGY. 1 13 



motes visible in the sunbeam. We now know how numerous 

 they must be*. 



In the case of parasitical worms, (the Distoma hepaticum, 

 for instance,) the ova are too large to be either conveyed by the 

 air, or to be absorbed by vessels from the food and carried to their 

 nidus in the viscera. Such worms have even been fovind in the 

 viscera of embryos. If we must have recourse to hypothesis to 

 account for the origin of these, let our hypothesis be supported 

 by analogy. It is not impossible that a portion of an ovum may 

 be able, as has been supposed by many, to germinate and pro- 

 duce a new individual, as a portion of a Polypus becomes a di- 

 stinct and perfect animal of its kindf. 



The opinion of the gradual production of all creatures from 

 an original simple form has received confirmation, in the minds 

 of many, from their having observed that the embryo of the 

 highest forms of life passes by gradations througli those which 

 are permanent in inferior animals. They have, however, sup- 

 posed this resemblance to be more complete than observation 

 allows us to believe it to be. We have seen that the first ob- 

 served embryo of all animals is extremely simple. With respect 

 to this simplicity, which but implies the imperfection of our tests, 

 a comparison may be allowed between embryos of a higher 

 order and the simplest forms of life, when the animal presents 

 no separation of distinct organs. As the development of the 



* " Although Dr. Ehrenberg, in refuting the notion of the extreme sim- 

 plicity of these animals, has overthrown one great ai'gument in favour of their 

 spontaneous origin, yet he has offered no explanation of their production in 

 infusions which have been subjected to a heat sufficient to destroy any parent 

 animals, or even ova, supposed to be present. In these cases, as is well known, 

 the adversaries of the theory ascribe the origin of Infusoria to ova conveyed by 

 the air ; an assumption which the supporters of the doctrine regard as highly 

 improbable, and which, if admitted as true, they consider 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 denying the pos- 

 sibility of its occui'rence, and discarding the theory of spontaneous generation 

 as unnecessary to account for the facts, it was incumbent on him to have sub- 

 jected anew to a rigid examination the observations of those who have arrived 

 at an opposite conclusion from himself, and either expose the fallacy of their 

 experiments, or show how they were to be explained 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." — Hr. Sharpey. Account of Professor Ehrenberg' s Researches 

 on the Infusoria: Edinb. New Phil. Journal, Oct. 1833. 



t Entozoa have been found in embryos and in the eggs of birds : so also 

 have pins and small pieces of flint. — Tiedemann's Anat. vnd Nat. Gesck. der 

 Vogel, b. ii. s. 128. quoted by Treviranus. 

 1834. I 



