kofoid: development of limax. 105 



the salt solution than in those under normal conditions. These later 

 proceeded to cleave normally, forming a new cavity after the cleavage, 

 which followed close on the obliteration of the cavity. The eggs in the 

 salt water did not divide, nor did a central cavity reappear, small len- 

 ticular spaces only being formed. All further activity seemed to be sus- 

 pended during the four hours that the eggs were kept under observation. 

 A portion of this lot was removed to fresh water after an exposure to 

 the salt solution for an hour and forty minutes. In the course of an 

 hour more cleavage took place, the cells passed through the rounded 

 and flattened conditions, but during the two hours in which the eggs 

 were observed no cavity appeared. These eggs seemed to be in a normal 

 condition on the following morning. Cleavage had not advanced in the 

 least in the eggs which remained in the 0.75% solution over night. 



The result of this experiment seems to show that the sudden transfer 

 of the eggs to the 0.75% salt solution is inimical to their further devel- 

 opment, and that it may have some influence in retarding the appearance 

 of the cleavage cavity when they are restored to fresh water. 



A trial of 0.38% salt solution gave approximately the same results. 



When, however, the eggs of both Physa and Amnicola were placed in 

 a 0.19% or 0.10% solution, cleavage was at first slightly delayed, occur- 

 ring from five to fifteen minutes later than in the control eggs in the 

 fresh water. After this initial delay, the cleavage seemed to progress in 

 both lots with equal rapidity. With regard to the cleavage cavity, 

 however, the two lots of eggs presented decidedly different results. 

 When the transfer was made to the salt solution a maximum cavity was 

 already present in both lots. Elimination occurred approximately at 

 the same time in both, but the subsequent reappearance of the cavity in 

 the eggs in the salt solution was delayed from fifteen to thirty minutes, 

 and it never reached the size of that in the eggs in the fresh water. 

 For example, the cavity in the control eggs attained a diameter of five 

 to seven units, while that of the eggs in the salt solution was only three 

 to four at the time of elimination. There were, however, a very few 

 cases in which the cavity reached a diameter of five units. 



These somewhat limited experiments seem to accord very well with 

 the observations on the cleavage cavity in fresh-water and marine forms, 

 and with the interpretation given to the cleavage cavity in the preceding 

 pages. They are also interesting in the light of Gruber's ('89) experi- 

 ments upon fresh- and salt-water Protozoa. When a species common to 

 both environments, as Actinophrys sol, is transferred from salt to fresh 

 water, there is a marked increase in the vacuolation of the protoplasm. 



