5(18 UNITY OK DESIGN. 



and a brain consisting of a longitudinal series of 

 tubercles ; next loosing its branchiae, and acquiring 

 lungs, while the circulation is yet single, and thus 

 imitating the condition of the reptile ; then ac- 

 quiring a double circulation, but an incomplete 

 diaphragm, like birds ; afterwards, appearing like 

 a quadruped, with a caudal prolongation of the 

 sacrum, and an intermaxillary bone ; and lastly, 

 changing its structure to one adapted to the erect 

 position, accompanied by a great expansion of the 

 cerebral hemispheres, which extend backwards so 

 as completely to cover the cerebellum. Thus does 

 the whole fabric arrive, by a gradual process of 

 mutation, at an extent of elaboration and refinement, 

 which has been justly regarded as constituting a 

 climax of organic developement, unattainable by 

 any other race of terrestrial beings.'^ 



It must, I think, be admitted that the analogies, 

 on which the hypothesis in question is founded, 

 are numerous and striking ; but great care should 

 be taken not to carry it farther than the just 



* A popular opinion has long prevailed, even among the well 

 informed, that mis-shapen or monstrous productions, or lusus 

 naturce, as they were termed, exhibit but the freaks of nature, who 

 was believed, on these occasions, capriciously to abandon her usual 

 course, and to amuse herself in the production of grotesque beings, 

 without any special object. But it is now found that all defective 

 formations of this kind are occasioned by the imperfect develope- 

 ment of some parts of the embryo, while the natural process is 

 carried on in the rest of the system ; and thus it happens that a 

 resemlilance may often be traced, in these malformations, with 

 the type or the permanent condition of some inferior animal. 

 Hence all these apparent anomalies are, in reality, in perfect 

 harmony with the established laws of organic developement, and 

 afford, indeed, striking confirmations of the truth of the theory here 

 explained. 



