12 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



in the adult bones, or in some embryonic condition 

 of the skeleton common to both animals. 



I have recently made a study of the development of 

 the breast-bone, and have realised the difficulties which 

 beset this subject in relation to the development of the 

 tissues in the embryo. Like the rest of the skeleton, the 

 sternum begins as myxomatous mesoblastic tissue. Its cells 

 become more closely conglomerated together to form a 

 longitudinal streak or strand of cells (associated at the 

 head end with the developing clavicle.) This cellular 

 band is joined by the ribs, and becomes converted into 

 hyaline cartilage, around which the formation of bone 

 occurs, gradually converting the cartilaginous sternum 

 into blocks of osseous tissue. 



I hope to have another opportunity this winter of 

 discussing the morphological questions connected with 

 this study. At present it is enough to point out how it 

 illustrates the depth of the difficulty surrounding the 

 evolution of any organism. Here we have a highly 

 complex process occurring not by chance, or apparently 

 on account of extraneous circumstances, but spon- 

 taneousty, and in consequence of the inherent vital 

 capacity of the constituent cells, due to the arrangement 

 of their atoms, to their chemical activity, in short, to the 

 functions of protoplasm. 



There appears to be more predestination than free 

 will in embryology, and not only the plan of the building, 

 but also the materials used are of a regular, definite 

 pattern. 



The Significance of Anatomical Variations. 



One of the strongest arguments in Darwin's theory 

 of the origin of species is the capacity of individual 

 organisms for variation. I would like for a moment to 



