SERRES 81 



doctrine of parallelism a complication enters. He observed 

 that embryonic organs did not always develop in a piece, by 

 simple growth, but often were formed by the union of 

 separately formed parts or layers. Thus the kidney in man 

 is formed by the fusion of a number of" little kidneys," and 

 the spinal cord reaches its full development by the laying 

 down of successive layers within it. He was greatly 

 impressed with this fact, which, as a convinced believer in 

 epigenesis, he used with great effect against the preformistic 

 theories. " This method of isolated formation," he wrote, " is 

 noticed in early stages in the thyroid, the liver, the heart, the 

 aorta, the intestinal canal, the womb, the prostate, the clitoris, 

 and the penis" (xi., p. 69). So, too, in the development 

 of the skeleton, ossification proceeds from separate centres, 

 foramina are formed by the fusion of separate bones round 

 them. In his memoir, Lois d'Osteogenie (1819), Serres 

 established several laws of ossification based upon this 

 principle of separate formation. 1 



How is the fact of multiple formation to be reconciled 

 with the principle of repetition, according to which organs are 

 simplest in the early embryo and in the lower animals? 

 But observation shows that, as a rule, the further down the 

 scale you go the more divided organs become the more 

 numerous the bones of the skull, for example. There is thus 

 a parallel between multiple formation of organs in the 

 embryos of the higher Vertebrates and their subdivided state 

 in the lower. Take, for example, the kidney. In the genus 

 Felts, and in birds, each kidney has two lobes, in the elephant 

 four, in the otter ten, in the ox twelve to fourteen. The 

 human kidney in its development starts with about a dozen 

 lobes, and the number diminishes as the kidney grows. 

 Thus the permanent state of the kidney in the animals 

 mentioned is reproduced by the stages of its development in 

 man (xii., p. 126). 



So, too, at the second or third month the uterus of the 

 human embryo is bicornuate, and afterwards passes through 

 stages comparable to the adult and permanent uterus of 

 rodents, ruminants, and carnivores. There is indeed a time 

 in the development of the human embryo when it resembles 

 1 See Radl, loc. cit., i.. pp. 225-6. 



