EMBRYOLOGICAL INVESTIGATIONS 265 



two first segmentation cells, or blastomeres, were 

 separated by shaking, each developed into a half- 

 larva, which actually became sexual, and which 

 ultimately regenerated the missing half by a process 

 of budding. 



Driesch, in 1891, carried out a similar but more 

 complete series of experiments at Trieste, employing 

 for the purpose the eggs of sea-urchins, chiefly 

 Echinus microtuberculatus and Sphcerechinus granu- 

 laris. Selecting eggs which had just completed the first 

 division, into two segmentation cells or blastomeres, 

 he put from fifty to a hundred in a small quantity 

 of sea-water in a glass tube about an inch and a 

 half long and a quarter of an inch in diameter. By 

 vigorously shaking the tube for five minutes or 

 longer he succeeded in rupturing the egg mem- 

 branes, and isolating the blastomeres. The contents 

 of the tube were then poured into a shallow vessel, 

 and the isolated blastomeres picked out with a fine 

 pipette, and placed in separate watch-glasses, in 

 which their further development could be followed. 

 Each blastomere so treated developed at first into 

 a half-embryo. By the evening of the first day a 

 hemi-blastula was formed. During the night a 

 change took place, and by the following morning 

 each hemi-blastula had become a complete blastula 

 or sphere, but of half the normal size. By the end 

 of the second day invagination commenced. Each 

 blastula became a gastrula in the normal manner ; 

 and the formation of the various organs, mouth, 

 arms, coelom, and ambulacral system was effected in 

 the typical fashion. In some cases the shaking had 



