CELL DIVISION IN EGGS OF CREPIDULA. 537 



but I must not fail to call attention at this place to the many general resem- 

 blances between my work and that of Konopacki (1911). 



In the course of this work 79 separate experiments were made on the effects 

 of hypertonic sea water on cell division in the eggs of Crepidula. In 60 of these 

 experiments the sea water was rendered hypertonic by the addition of NaCl in 

 varying quantities; in the remaining experiments MgCl 2 , KC1, or cane sugar were 

 added to sea water. In all cases percentage solutions were used. After having 

 been subjected to the action of these solutions for varying lengths of time the 

 eggs were either fixed at once or were placed in normal sea water for a longer or 

 shorter period before being fixed. All the eggs used in each experiment were 

 stained and mounted, and most of them were studied, though not one in a 

 thousand are represented in the drawings. 



The results obtained in any given experiment may be extremely varied, 

 depending to a considerable extent upon the general stage of development of 

 the eggs, and upon their precise stage in the cycle of cell division at the time the 

 eggs were put into the salt solution. Early stages of development are always 

 more susceptible to any kind of environmental change than are later ones; and 

 stages during kinesis are much more susceptible than are those during inter- 

 kinesis. In particular the first and second cleavages are most easily modified 

 and seem to be especially unstable. 



My observations confirm the conclusions of Loeb and others that there is 

 nothing specific in the action of any one of the salts named; where all other 

 conditions are similar, essentially the same results are obtained, whatever 

 salt is used. Therefore the results of these experiments will be described under 

 the types of abnormalities produced rather than under the particular salts 

 employed. With different salts, different strengths of solution are necessary to 

 produce similar results. In Y 2 per cent. NaCl and 1 per cent. MgCl 2 all division 

 goes on slowly, but typically (Exps. 861, 866); while Y 2 per cent. KC1 (Exp. 847) 

 produces certain abnormalities. In 1 per cent. NaCl (Exps. 804, 808, 988, 989, 

 994), % per cent. KC1 (Exp. 836), and 2 per cent. MgCl 2 (Exps. 833, 841) yolk 

 division is stopped, especially in the first and second cleavages, while centrosomal, 

 nuclear and cytoplasmic division may proceed slowly and more or less atypically. 

 In 2 per cent. NaCl (Exps. 805, 809, 969, 970), 1 per cent. KC1 (Exp. 837), 4 per 

 cent. MgCl 2 (Exps. 842, 846) all division, nuclear as well as cytoplasmic, ceases 

 while the eggs are in the solutions, and if left in these solutions for approximately 

 9 hrs. this stoppage of all divisional phenomena is permanent, even when the 

 eggs are returned to normal sea water, although the eggs may remain alive and 

 the nuclei may continue to grow in size. 



Morgan (1899) discovered that weak solutions acting for a long time are 

 similar in effect to strong solutions acting for a short time. My work confirms 

 this conclusion, but only in cases where the solutions are strong enough to inhibit 

 all divisional phenomena during the time the eggs are in the salt solutions. 

 If solutions are weak enough to allow any of the parts of a cell to divide, the time of 



