20 PROCEEDINGS OF THE ACADEMY OF [Jan., 



when the ratio chromosomes to protoplasm reaches a certain con- 

 stant. Increase of the mass of the chromosomes retards cell division, 

 which does not occur until the mass of the protoplasm increases 

 also. The material for the growth of the chromosomes is furnished 

 by the protoplasm, from its "reserve material," according to Sachs. 

 So cell growth consists in the transformation of protoplasmic into 

 chromatin material in the nucleus until a definite ratio of P : C = k 

 is reached, when division occurs. The mother cell just before divis- 

 ion consists of nC-j-P = M. After division M divides into 2D 

 each being nC'-r-P'. These daughter cells then grow to the size 

 and ratio of the mother cell, or until nC'-i-P' becomes nC-^P, 

 when division may again occur. Starvation produces a reduction 

 in the amount of protoplasm and retards the development of the 

 chromosomes. ^Estivation will cause reduction in the amount of 

 protoplasm and retard cell division. J. Sachs was the first to point 

 out that in each species the ultimate size of the cell is a constant 

 for each organ and that wfiere two individuals differ in size, the differ- 

 ence is in the number and not the size of corresponding cells. 

 Amelung, a student of Sachs, confirmed this by actual count. But 

 it seems probable that diminution in the amount of protoplasm 

 may be accompanied or followed by a reduction in the mass of the 

 chromosomes and reduction in the size of the nuclei, and as the ratio 

 C-i-P is constant for cell division, then C-j-P = M by reduction of 

 mass of both C and P to C and P' becomes C'-i-P' = M', a smaller 

 cell. It is in this way that the observed reduction in size of the 

 embryonic shell or protoconch in these dwarfed forms of the two 

 species of Lucidella here considered is to be explained. For this 

 reduction in size of the protoconch must accompany a reduction 

 in the size of the egg, and it is probably the establishing of a new 

 equilibrium resulting in the reduction in size of the egg (among 

 other things) that is the explanation of the observation that condi- 

 tions unfavorable to the growth of the animal are not unfavorable 

 to its reproduction. 



Explanation of Plate I. 



It i s to be noted that figures 1-6 are enlarged somewhat more than the rest, 

 being magnified 4.5 times, while all the other figures (7-26) are magnified 3.4 

 times, and these being all on the same scale, the relative sizes may be directly 

 compared. Figs. 7-10 are normal; 11-15 are dwarfed; figs. 16-21 are normal; 

 22-26 dwarfed. 



Figs. 1, 2, 3. — Lucidella granulosa C. B. Adams (Swift Collection). Showing 

 the tuberculated and keeled periphery characteristic of the specimens in 

 this lot. 



