450 



-SY 7>'-/7/} 'LUM CEPHALOCHORDA. 



ments of one side are not opposite those of the other, and 

 so on. By the process known as the " symmetrisation " of 

 the larva, the apparent symmetry of the adult is produced. 

 The adult position of the anus and of the olfactory pit, 



-nc 



nip 



FlG. 222. Sections through embryos of A mph io.vus, to 

 illustrate development of body cavity. 



On the upper line, three longitudinal sections ; on the lower line, 

 three transverse sections. ec~., Ectoderm; en., endoderm ; ., 

 archenteron ; p.s., primitive segments (protovertebrae) ; n.c., 

 nerve-cord;/., posterior end; n/>., neuropore ; ne.c., neuren- 

 teric canal ; in.p., medullary or neural plate ; c/i., notochord ; 

 ep.i splanchnocoel, above it is the myocoel. 



both to the left side, and the position of the unpaired liver 

 diverticulum, show how partial this process is. 



Experimental embryology. As an illustration of experimental em- 

 bryology, and of the developmental potentiality of the early segmentation 



