ORGANIC DEVELOPMENT. 431 



vided only for this temporary use appears from the circum- 

 stance of its falling off spontaneously in the course of three 

 or four days after it has been so employed. 



But though the bird has now gained its liberty, it is still 

 unable to provide for its own maintenance, and requires to 

 be fed by its parent till it can use its wings, and has learned 

 the art of obtaining food. The pigeon is furnished by na- 

 ture with a secretion from the crop, with which it feeds its 

 young. In the Mammalia the same object is provided for 

 still more expressly, by means of glands, whose office it is 

 to prepare milk, a fluid which, from its chemical qualities, 

 is admirably adapted to the powers of the digestive organs, 

 when they first exercise their functions. The Cetacea have 

 also mammary glands; bwt as the structure of the mouth and 

 throat of the young in that class does not appear adapted to 

 the act of sucking, there has always been great difficulty in 

 understanding how they obtain the nourishment so pro- 

 vided. A recent discovery of Geoffroy St. Hilaire appears 

 to have resolved the mystery with respect to the Delphinus 

 globiceps; for he found that the mammary glands of that ani- 

 mal contain each a large reservoir, in which milk is accu- 

 mulated, and which the dolphin is capable, by the action of 

 the surrounding muscles, of emptying at once 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 deve- 

 lopment in the higher animals, taken in conjunction with the 

 facts already adverted to in various parts of this Treatise, 

 and particularly those relating to ossification, dentition, the 

 formation of hair, of the quills of the porcupine, of the an- 

 tlers 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 



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

 at the "Institut." March 24, 1834. 



