116 HYPOTHESIS OF THE DEVELOPMENT OF 



preceding illustrations in a form calculated to bring them 

 more forcibly before the mind of the reader. The follow- 

 ing table was suggested to me; in consequence of seeing 

 the scale of animated nature presented in Dr. Fletcher's 

 Rudiments of Physiology. Taking that scale as its basis, 

 it shows the wonderful parity observed in the progress of 

 creation as presented to our observation in the succession 

 of fossils, and also in the foetal progress of one of the prin- 

 cipal human organs.* This scale, it may be remarked, 

 was not made up with a view to support such an hypo- 

 thesis as the present, nor with any apparent regard to the 

 history of fossils, but merely to express the appearance of 

 advancement in the orders of the Cuvierian system, as- 

 suming, as the criterion of that advancement, '« an in- 

 crease in the number and extent of the manifestations of 



* 81 It is a fact of the highest interest and moment that as the 

 brain of every tribe of animals appears to pass, during its develop- 

 ment, in succession through the types of all those below it, so the 

 brain of man passes through the types of those of every tribe in the 

 creation. It represents, accordingly, before the second month of 

 utero-gestation, that of an avertebrated animal ; at the second 

 month, that of an osseous fish ; at the third, that of a turtle ; at 

 the fourth, that of a bird : at the fifth that of one of the rodentia ; 

 at the sixth, that of one of the ruminantia ; at the seventh, that of 

 one of the digitigrada ; at the eighth, thai of one of the quadrumana ; 

 till at length, at the ninth, it compasses the brain of Man ! It is 

 hardly necessary to say, that all this is only an approximation to 

 the truth ; since neither is the brain of all osseous fishes, of all 

 turtles, of all birds, nor of all the species of any one of the above 

 order of mamals, by any means precisely the same, nor does the 

 brain of the human foetus at anytime precisely resemble, perhaps, 

 that of any individual whatever among the lower animals. Never- 

 theless, it may be said to represent, at each of the above-mention- 

 ed periods, the aggregate, as it were, of the brains of each of the 

 tribes stated ; consisting as it does, about the second month, chiefly 

 of the mesial parts of the cerebellum, the corpora quadrigemina, 

 thalami optici, rudiments of the hemispheres of the cerebrum and 

 corpora striata ; and receiving in succession, at the third, the ru- 

 diments of the lobes of the cerebrum ; at the fourth those of the 

 fornix, corpus callosum, and septum lucidum ; at the fifth ; the tu- 

 bor annulare, and so forth the posterior lobes of the cerebrum in 

 creasing from before to behind, so as to cover the thalami optici 

 about the fourth month, the corpora quadrigemina at >ut the sixth 

 and the cerebellum about the seventh. This, then, is another ex 

 ample of an increase in the complexity of an organ succeeding its 

 centralization ; as if nature, having first piled up her materials in 

 3iie spot, delighted afterwards to employ her abundance, not so 

 much in enlarging old parts as in forming new ones upon the old 

 foundations, and thus adding to the complexity of a fabric the ru- 

 dimental structure of which is in all animals equally simple." - 

 Fletcher's Rudiments of Physiology. 



