ORGANIC DEVELOPEMENT. 617 



into the mouth of its young, without requiring 

 from the latter any effort of suction.* 



The rapid sketch which I have attempted to 

 draw of the more remarkable steps of the early 

 stages of organic developement in the higher 

 animals, taken in conjunction with the facts al- 

 ready adverted to in various parts of this Trea- 

 tise, and particularly those relating to ossifica- 

 tion, dentition, the formation of hair, of the quills 

 of the porcupine, of the antlers of the stag, and 

 of the feathers of birds, will suffice to show that 

 they are regulated by laws which are definite, 

 and preordained according to the most enlarged 

 and profound views of the future circumstances 

 and wants of the system. The double origin of all 

 the parts of the frame, even those which appear 

 as single organs, and the order of their forma- 

 tion, which, in each system, commences with the 

 parts most remote from the centre, and proceeds 

 inwards, or towards the mesial plane, are among 

 the most singular and unexpected results of this 

 train of inquiries. t We cannot but be forcibly 



* The account of this discovery is contained in a memoir which 

 was read at the " Institut." March 24, 1834. 



t The first of these two laws is termed by Serres, who has 

 zealously prosecuted these investigations, " la loi de sy mmctrie ;" 

 and the second, " la loi de conjugaison." He maintains that 

 they are strictly applicable to all the parts of the body having a 

 tubular form, such as the trachea, the Eustachian tube, the canals 

 and perforations of bones, &c. See the preliminary discourse to 



