DEVELOPMENT, ETC. OF ORGANIZATION. 99 



of metamorphosis; thus the membranes of the ovum and the 

 placenta, the pupillary membrane, the milk teeth cease to ex- 

 ist, and the surrenal capsules and the thymus gland, greatly 

 diminish, and finally, almost totally disappear. 



106. The organs and humours are not always in the same 

 proportion. In the beginning the embryo is nothing but a 

 nearly liquid molecule ; in time the proportion of solids in- 

 creases and continues to augment till the end. The colour is 

 also gradually developed; at first all the parts are white, the 

 colouring of the blood and other parts takes place, by degrees. 

 There is at first no determined texture in the organs: there is 

 even no globules in the beginning, while at a later period, the 

 whole mass of the body appears, globular, or granulated, after 

 which fibres, lamina and vessels become distinct. All the 

 organs are not developed at one time. Even those of the 

 same genus or system are not all formed together. The ex- 

 ternal form or configuration is drawn before the consistence, 

 texture and composition are fixed; for, as we see in the fruit 

 of the almond which has already its form, and is as yet a mere 

 glairy liquid which will successively acquire the consistence, 

 texure and composition proper to it, so the nervous and bony 

 systems already have partly their form while yet liquid. The 

 cellular tissue; and the vessels permeable by liquids, diminish 

 from the beginning to the end of life; it is, above all, this 

 change which continues after the end of the growth, that essen- 

 tially appears to constitute the period of the deterioration of 

 the organism and of old age. 



107. The organs are formed by separate parts that after- 

 wards unite; thus the nervous medulla is at first a double 

 cord ; the intestine and the cavity of the trunk, at first open 

 in front, afterwards close it is also the same with the spinal 

 canal. The vessels, at first, are isolated vesicles which stretch 

 and communicate in the mass of the body : the kidneys, at first 

 multiple, coalesce and adhere; the bones which in the carti- 

 lagenious state, lengthen themselves by a species of vegeta- 

 tion, afterwards become ossified in separate parts which then 

 unite, &c. Traces of this formation, remain in certain places, 

 stronger in some, weaker in others; thus the raphe of the skin, 



