684 president's address. 



account for a return to a certain shape after the under^^oing of 

 active or passive changes of form 1 



When the vesicular theory of cell-structure is applied to the 

 nucleus it meets with still greater difficulties. Flemming*' has 

 lately protested against the view that the appearances in nuclei 

 described by himself and others are due to post-mortem changes. 

 In the living condition, in very many cases the nucleus appears 

 quite clear and devoid of structure, except that perhaps a nucleolus 

 may be distinguishable. The internal structure only becomes 

 visible gradually if no re-agents are employed, more suddenly 

 under the action of acetic acid. The structure becomes visible 

 only post-mortem, but is not to be regarded on that account as 

 artificial. Under the action of acetic acid the granules and 

 threads start into view in a manner which proves that they cannot 

 be formed by movement and re-arrangement of the nuclear 

 substance. And in some nuclei these structures are visible in the 

 living condition of the cell without the use of re-agents. 



But the difficulties in the way of aecepting Biitschli's conclusions 

 as sufficient become most manifest when we consider the case of the 

 ovnm. It is difficult to be satisfied with a view of cell-structure 

 which would lead to the conclusion that the difference between 

 the ovum of an Echinoderm and that of a Mammal is merely a 

 difTerence in the chemical composition of the protoplasm, and, 

 •structurally, in the size and disposition of the bubbles or vesicles. 

 To account for the differences in the developmental history we 

 need something, call it what you may — physiological molecule, 

 micella, idioblast — between the chemical molecule and the vesicle, 

 something the special properties of which determine the direction 

 of the development. 



Altmannf has recently published a short paper which may be 

 regarded as a supplement to his work " Die Elementarorganismen 

 und ihre Beziehungen zu den Zellen," issued two years ago. He 



* " Ueber Unsichtbarkeit lebendiger Kernstrukturen." Anat. Ar.zeiger, 

 1S92. 



+ " Ein Beitrag zur Granulalehre." Verhandl. Anat. Gesellsch. 1892, 

 pp. 220-223. 



