116 DEVELOPMENT OF THE FROG'S EGG [On. XI 



under the conditions of Roux's experiment. The subsequent 

 postgeneration of the injured half of the egg has also been 

 studied by these authors. They confirm in every detail the 

 method of reorganization and postgeneration of the injured 

 half as described by Roux. The reorganizing cells have migrated 

 from the uninjured to the injured side, and there have caused the 

 protoplasm to break up into cells. The injured blastomere is 

 also overgrown directly by the ectoderm of the uninjured and 

 developing side. In many of these embryos the right and 

 left side (one side has postgenerated) are separated from each 

 other by a protruding yolk-mass, forming spina-bifida embryos. 

 The reorganization of the much changed mass of the injured 

 blastomere is brought about by being assimilated by the cells 

 that have migrated into that region, by the second and third 

 methods of reorganization described by Roux. When the mate- 

 rial of the injured half is only incompletely reorganized, there 

 is formed, after postgeneration, a more or less pronounced spina 

 bifida. When the injured material is completely worked over 

 or reorganized and postgenerated, a perfect embryo may be 

 formed. 



Schultze ('94, b, d) has made an interesting modification of 

 one of the experiments of Pfluger and obtained most unex- 

 pected results. The eggs of Rana fusca removed from the 

 uterus were placed singly upon slides. On each slide had 

 been stuck two thin glass rods from 1.65 to 1.35 mm. in thick- 

 ness. Between these rods, which are separated from each other 

 by the width of the slide, an egg is placed with the white pole 

 uppermost. The egg is then fertilized in this position. After 

 three minutes the spermatozoa may be supposed to have entered, 

 and a glass cover is placed over the egg and brought down into 

 contact with the two glass rods above-mentioned, and there 

 fixed with rubber rings. The egg is by this means slightly 

 compressed and held more or less firmly in position. Each 

 slide is then turned over, i.e. through 180 degrees, so that the 

 dark pole of the compressed egg is brought upward. The 

 eggs now in the normal position are put into a dish of water, 

 to remain in this position until the jirst furrow has appeared or 

 even until it has passed through the egg. Then the slide and 



