248 ifr Sedgtuick, On the Cell Theory and Nerves. [Nov. 26, 



These points determine the positions of the lines numbered 

 1 to 12. The lines 18, 14, 15 can be found by the method 

 described in Art. 1. 



Since however the lines numbered 16 to 27 do not occur in any 

 triangle with two other known lines, that is, those numbered from 

 1 to 12, the method now fails. 



Therefore, since we know that 16 meets 1, 4, 7, 10 and 14 we 

 can draw these lines on paper, or arrange them on a model, and 

 find the position of 16 by a method of adjustment. 



When 16 is found, the remaining lines can be determined in 

 the former way. 



[0?i a special foi'in of the General Equation of a Cubic Surface 

 hy H. M. Taylor, M.A. Philosojjhical Transactions of the Royal 

 Society of London, Vol. 185. (1894).] 



(3) Exhibition of some photographs shewing the marks made 

 hy stars on photographic plates exposed near the focus of a visual 

 telescope. By H. F. Newall, M.A., Trinity College. 



[See Monthly Notices, R. Astron. Soc, Vol. liv.] 



November 12, 1894. 



Professor J. J. Thomson, President, in the Chair. 



The following Communications were made to the Society: 



(1) On the inadequacy of the Cell Theory and on the develop- 

 ment of Nerves. By A. Sedgwick, M.A., Trinity College. 



The author pointed out that the cell-theory in so far as it 

 implied that the organism was composed of cell-units derived by 

 division from a single primitive cell-unit, the ovicell, would not 

 bear the scrutiny of modern embryology, and that in fixing men's 

 attention too much upon the cell as a unit of structure, it had had 

 a retarding influence on the progress of the knowledge of struc- 

 ture. He iUustrated this latter point hy reference to the current 

 ideas on two important subjects : the structure of the embryonic 

 tissue called mesenchyme, and the development of nerves. The 

 mesenchyme is not composed of separate branched cells, but has 

 rather a spongy or reticulate structure, and is continuous both 

 with ectoderm and endoderm. Nerves do not develop as out- 

 growths of the central organ, but arise in situ from the mesen- 

 chyme. 



(2) Note on the evolution of gas by luater-plants. By F. 

 Darwin, MA., Christ's College. 



