FREE BOOKS

Author's List




PREV.   NEXT  
|<   219   220   221   222   223   224   225   226   227   228   229   230   231   232   233   234   235   236   237   238   239   240   241   242   243  
244   245   246   247   248   249   250   251   252   253   254   255   256   257   258   259   260   261   262   263   264   265   266   267   268   >>   >|  
, the facts of the case, so far as the skate is concerned, assuredly do appear to sanction the doctrine of "prophetic germs." The organ in the skate seems to be on its way towards becoming such an organ as we meet with in these other animals; and, therefore, unless we can show that it is now, and in all previous stages of its evolution has throughout been, of use to the skate, the facts do present a serious difficulty to the theory of natural selection, while they readily lend themselves to the interpretation of a disposing or fore-ordaining mind, which knows how to construct an electric battery by thus transforming muscular tissue into electric tissue, and is now actually in process of constructing such an apparatus for the prospective benefit of future creatures. Should it be suggested that possibly the electric organ of the skate may be in process of degeneration, and therefore that it is now the practically functionless remnant of an organ which in the ancestors of the skate was of larger size and functional use--against so obvious a suggestion there lie the whole results of Professor Ewart's investigations, which go to indicate that the organ is here not in a stage of degeneration, but of evolution. For instance, in _Raia radiata_, it does not begin to be formed out of the muscular tissue until some time after the animal has left the egg-capsule, and assumed all the normal proportions (though not yet the size) of the adult creature. The organ, therefore, is one of the very latest to appear in the ontogeny of _R. radiata_; and, moreover, it does not attain its full _development_ (i. e. not merely _growth_, but transforming of muscular fibres into electrical elements) till the fish attains maturity. Read in the light of embryology, these facts prove, (1) that the electric organ of _R. radiata_ must be one of the very latest products of the animal's phylogeny; and, (2) that as yet, at all events, it has not begun to degenerate. But, if not, it must either be at a stand-still, or it must be in course of further evolution; and, whichever of these alternatives we adopt, the difficulty of accounting for its present condition remains. In this connexion also it is worth while to remark that the electric organ, even after it has attained its full _development_, continues its _growth_ with the growth of the fish, and this in a much higher ratio, either than the tail alone, or the whole animal. Lastly, Prof. Burdon Sanderson
PREV.   NEXT  
|<   219   220   221   222   223   224   225   226   227   228   229   230   231   232   233   234   235   236   237   238   239   240   241   242   243  
244   245   246   247   248   249   250   251   252   253   254   255   256   257   258   259   260   261   262   263   264   265   266   267   268   >>   >|  



Top keywords:

electric

 

muscular

 
tissue
 

growth

 

evolution

 

animal

 

radiata

 
difficulty
 

latest

 

present


degeneration

 

development

 

process

 
transforming
 
fibres
 

elements

 

electrical

 
attains
 

creature

 

assumed


normal
 

proportions

 
capsule
 

attain

 

ontogeny

 

maturity

 

remark

 

attained

 

continues

 
remains

connexion

 

higher

 

Burdon

 
Sanderson
 

Lastly

 
condition
 
accounting
 

phylogeny

 

events

 
products

embryology

 
degenerate
 
whichever
 

alternatives

 

functional

 

natural

 

selection

 
theory
 
stages
 

readily