106 POURTH REPORT — 1834. 



been intended by their concurrent acts to produce the phaeno- 

 mena of life, could scarcely lead to the detection of that control- 

 ing cause whicii forced the whole to conspire to a common pur- 

 pose. It became necessary, therefore, to consider the subject 

 imder a different aspect ; to contemplate living bodies in their 

 approach towards the possession of those powers which they ex- 

 hibit when their organs are formed. The means for this have 

 been supplied by the labours, extended through a long lapse of 

 time, of Harvey, of Malpighi, of the Hunters, of G. F. Wolff, of 

 Prevost and Dumas, of Meckel, of Tiedemann, of Serres, of G. 

 de St. Ililaire, of Von Baer. The earliest examinations that 

 can be made of plants or of animals present them as consisting 

 of a minute globule of fluid, or a minute disc of slightly albumi- 

 nous matter, i. e. under aspects not distinguishable in different 

 future genera or species, as to properties or forms of their matter, 

 by any tests which we possess. In the near neighbourhood of 

 the disc is placed, in animals, a quantity of nutritive substance, 

 by means of which it is destined to work. The effects, when 

 produced, are definite for each species ; but none occur except 

 under certain conditions. These conditions are, a due degree of 

 moisture, of air, and of warmth. When they are supplied, the 

 disc is capable of being affected by the matter in its neighbour- 

 hood. It is excited, and it reacts. The consequence of the re- 

 action is a gradual expansion of the disc to surround the nutrient 

 matter ; a separation of it into different superposed portions, 

 which come into view; and a gradual appropriation of the nutrient 

 matter. Upon the external portion of the disc, the first trace of 

 the nervous system is observed ; upon the internal portion, that 

 of the intestinal canal ; intermediate betw^een them, that of the 

 vascular system. Though at first simple, these objects have still 

 a certain magnitude, and the later more complex formations are 

 seen to arise from them as if by vegetation. " The first trace of 

 the nervous system is not merely that of the spinal cord or of 

 the ganglionic string, but is the potential whole of that system, 

 of the brain and all its appendages. The first trace of the ab- 

 dominal canal is not merely the rudiment of that canal, but of 

 the w^hole glandular apparatus also, which may be seen gradually 

 to spring from it*." And thus is the observed process of de- 

 velopment altogether contradictory of the theory of Haller and 

 of Bonnet, which represents each organ as absolutely existing in 

 the germ, though in a miniature form. That the power which 

 effects these changes, and thus controls the disposition of or- 

 ganic molecules, resides in the disc, is ascertained from the facts, 



* Mullcr's PlnjFAologij, vol. i. p. 20 ct ^q. 



