502 T. H. Morgan. 



of the body. That the early development depends on the proto- 

 plasm, and not on the nucleus, as previous theories had assumed, 

 was first demonstrated by Driesch and myself by means of an 

 experiment on the unsegmented ctenophore-egg, from which a 

 part of the protoplasm was removed but the entire nucleus left. 

 Defects appeared in the embryo. Later observers have con- 

 firmed the conclusions that we drew from our experiment and 

 have greatly extended the results. The observations of Wilson 

 and of Conklin have been especially interesting in showing that 

 extensive processes of protoplasmic migration may occur. Fur- 

 thermore the results of Wilson and of Yatsu have shown that the 

 localization of the materials takes place only after the germinal 

 nucleus of the egg breaks down. Even in such eggs as the sea 

 urchin there is evidence of a similar localization.^ Although in 

 this egg and in some other eggs the totipotence of the diff^erent 

 regions often so overbalances the difference of the parts that 

 isolated portions of the egg do not show strikingly the evidence of 

 the specification of their materials. 



Since the different regions of the adult animal are formed out of 

 the different materials of the egg, which must be assumed to increase 

 enormously in volume as the animal grows larger, we must sup- 

 pose that these different materials furnish the basis for the regen- 

 eration of the same organs. In many animals the gradation in the 

 amount of each kind of substance may be very gradual and extend 

 throughout almost the entire length of the body, e. g., in Lumbri- 

 culus, as shown in that a head or a tail may regenerate from any 

 level. If on the other hand sharp regional differences exist, such 

 as that between a leg and the body of an animal, we may expect 

 to find a corresponding limitation in the regenerative capacity, 

 so that the leg is no longer capable of making a body, etc. 



Even where the material is proliferated at the cut surface to 

 make the new part, as happens in many cases of regeneration, 

 the gradation of the material of the old part still maintains — 

 that first produced coming from the more distal end and that 

 produced later coming from further in, from the more proximal 

 parts — but the formative action must be supposed to take place 

 not only under the influence of the new material, but of the 

 neighboring parts as well. 



^Driesch ('oo); Boveri ('oi); Morgan ('oi). 



