30 THE GROWTH OF THE BRAIN. 



the volume of the egg. The tiny gastula thus produced 

 is composed of small cells, but not cells proportionately 

 reduced in size, since they may have five times the 

 volume of the cells composing the normal gastula. 



Multiple embryos from a single egg have been 

 obtained by Loeb 1 in yet a different way. This investi- 

 gator has succeeded in causing eggs, just fertilised, but 

 still undivided, to swell so that the enclosing membrane 

 ruptured, and a portion of the cell contents extruded 



FIG. 6. Multiple embryos from sea-urchin eggs, X 94 diam. 

 (Loeb), I twin, 2 triplet. 



in the form of one or more buds or droplets. In due 

 season these buds, as well as the cell substance remain- 

 ing within the membrane, developed embryos. The 

 multiple embryos thus formed are represented in the 

 accompanying figure. Thus, where at the start the egg 

 was morphologically but a single cell, it has been found 



1 Loeb, vide Biological Lectures, delivered at Wood's HolL 

 Boston, 1894. 



