DUPARTMUNT OF MARINE) BIOLOGY. I3I 



relation of calcium to cytolysis shows further that it is not present in the egg 

 in the same condition as in sea-water and does not pass into the egg in that 

 condition, but does do so the moment swelling of the egg begins. 



The conception of cytolysis to which I have been led is essentially that 

 of Hamburger, Koeppe, and other physiologists. It is certain that during 

 cytolysis there is a progressive change from complete impermeability to com- 

 plete permeability for most diffusible substances ; for it is a change from a 

 definite plasma membrane to no true surface whatsoever if the eggs remain 

 in the solution long enough. 



The apparent surface of cytolized eggs is in reality merely the artificial 

 fertilization membrane formed by the cytolytic substance in the first stages 

 of cytolysis. The permeability of the plasma membrane is increased to a cer- 

 tain extent, and under these conditions substances pass out which form an 

 albuminoid membrane. In the next stage the egg-surface becomes permeable 

 to the salts of sea-water when swelling and disintegration of the granules 

 takes place, and at the same time the egg-surface loses its continuity. The 

 cause of the swelling is simply the substitution of a surface freely permeable 

 to salts in place of one quite impermeable to them. 



In the normal egg the sum of the osmotic pressures of the substances 

 within the egg just counterbalances that of the salts of sea-water. This does 

 not mean that the substances within the egg are the same as those without. 

 The egg is not a mass of proteid saturated with sea-water, but its salt content 

 is different. Suddenly the membrane separating these two phases becomes 

 permeable for the dissolved substances of one phase but not for those of the 

 other. The result is the same as placing the cell in distilled water. It swells 

 until its turgor pressure is balanced by the tension of its artificial membrane. 



The slowness with which eggs swell when placed in distilled water, con- 

 sidering the large surface area, points to the view that even water encounters 

 resistance in its exit from and entrance into the egg. In distilled water the 

 egg slowly swells to a certain size, at which point it suddenly swells and a 

 delicate membrane forms. I am inclined to believe that at this point the 

 surface becomes freely permeable to the entrance of water, at the same time 

 losing its continuity, and the whole egg swells (within the artificial mem- 

 brane which forms) until its internal pressure is compensated by the tension 

 of its membrane. 



Preliminary Report on Reactions to Light in Marine Ttirbellaria, by 

 S. 0. Mast, Goiicher College, Baltimore. 



Four different species of marine turbellaria were used in the experiments 

 on reactions to light, performed at the Tortugas Laboratory, during the latter 

 part of June and the first part of July 1910. The reactions in all of these 

 species are essentially the same. Under favorable conditions they orient and 

 move fairly accurately from the light if there is but a single source. There 

 is, at least in many instances, no indication of preliminary trial in the process 

 of orientation. If light strikes these animals from one side they ordinarily 

 turn directly from the side most highly illuminated. If they are exposed to 

 light from two sources they proceed from a point between these two sources ; 

 but the location of this point depends upon the relative intensity of the light 

 which comes from each of the two directions. 



The chief object of this work was to ascertain: (i) the function of the 

 eyes in the reaction of the turbellaria to light, and (2) the nature of the 

 stimulus. 



