EXPERIMENTAL MORPHOGENESIS 53 



highest optical powers, is the foundation of all morpho- 

 genetic processes, in such a way that, whilst part of this 

 structure is handed over from generation to generation as 

 the basis of heredity, another part of it is disintegrated 

 during the individual development, and directs development 

 by being disintegrated. The expression, " part " of the 

 structure, first calls for some explanation. Weismann 

 supposes several examples, several copies, as it were, of his 

 structure to be present in the gerni cells, and it is to these 

 copies that the word " part " has been applied by us : at least 

 one copy has to be disintegrated during ontogeny. 



The morphogenetic structure is assumed to be present in 

 the nucleus of the germ cells, and Weismann supposes 

 the disintegration of his hypothetic structure to be accom- 

 plished by nuclear division. By the cleavage of the egg, 

 the most fundamental parts of it are separated one from 

 the other. The word " fundamental ' must be understood 

 as applying not to proper elements or complexes of 

 elements of the organisation, but to the chief relations 

 of symmetry ; the first cleavage, for instance, may separate 

 the right and the left part of the structure, the second one 

 its upper and lower parts, and after the third or equatorial 

 cleavage all the principal eighths of our minute organisa- 

 tion are divided off: for the minute organisation, it must 

 now be added, had been supposed to be built up differently 

 in the three directions of space, just as the adult organism 

 is. Weismann concedes it to be absolutely unknown in 

 what manner the proper relation between the parts of the 

 disintegrated fundamental morphogenetic structure and the 

 real processes of morphogenesis is realised ; enough that there 

 may be imagined such a relation. 



