TKE ARGUMENTS FROM EISIBRYOLOGY. 375 



Let US now return to the development of individual 

 organisms ; carrying back this idea with us. On the 

 hypothesis of evolution, all organs must have been originally 

 formed after the indirect method, by the accumulation of 

 modifications upon modifications ; and if the development of 

 the embryo repeats the development of ancestral races, 

 organs'^must be thus formed in the embryo. To a consider- 

 able extent they are thus formed. There is a striking 

 parallelism between the mode in which, as above described, 

 manufacturing agencies are originally evolved, and the 

 mode in which secreting organs are evolved. Out of the 

 group of bile-cells forming the germ of the liver, some 

 centrally-placed ones, lying next to the intestine, are trans- 

 formed into ducts through which the secretion of the peri- 

 pheral bile-cells is poured into the intestine ; and as the peri- 

 pheral bile-cells multiply, there similarly arise secondary 

 ducts emptying themselves into the main ones ; tertiary ones 

 into these ; and so on. But while in this and in other 

 organs, the development remains in a great degree indiiect ; 

 there are organs, as the heart, in which it is comparatively 

 direct. The heart of the vertebrate embryo does not arise 

 from a bud ; but it is first traceable as an aggregated mass 

 of cells, becoming distinct from the cells amid which it is 

 imbedded : its transformation into a contractile chamber, is 

 effected by the consolidation of its outer cells while its inner 

 cells liquify. And the comparatively direct development 

 thus displayed in some organs of the higher embryos, is, as 

 we have seen, characteristic of the entire development in 

 many lower embryos. 



On the hypothesis of evolution, the direct mode of de- 

 velopment in animals, must have been substituted for the 

 indirect mode ; as we see that it is substituted in societies. 

 How comes it to have been substituted ? By studying the 

 cause of the substitution in the social organism, we may 

 perhaps get some insight into its cause in the individual or- 

 ganism. The direct mode of forming social agencies 



