MEMBRANE FORMATION AND CYTOLYSIS 



183 



outflow of a clear substance from the cytoplasm (Fig. 50), 

 and soon after the egg is changed to a shadow (Fig. 51). 



In this case also the process of cytolysis is divided into two 

 stages, at first, a membrane formation, and soon after a complete 

 clarification of the interior and the formation of large clear 

 drops (Fig. 51). 



If the eggs are placed in a mixture of 10 c.c. of sea-water -h 

 10 c.c. 2J m propylalcohol, the formation of a fertilization mem- 

 brane is the first thing that takes place. If the eggs are removed 



Fig. 52 Fig. 53 



FIGS. 52 and 53. Membrane formation and cytolysis in two different eggs 

 of a sea-urchin under the influence of propylalcohol. In Fig. 52 cytolysis starts 

 with the outflow of many small droplets ; in Fig. 53 with the outflow of only one 

 large drop from the cytoplasm. 



from the solution at this stage, and washed with sea-water, a 

 few are able to develop after a subsequent exposure to hyper- 

 tonic sea-water. 



But if the eggs are left in the solution of alcohol, cytolysis 

 quickly ensues. Figs. 52 and 53 show the start of this cytolysis 

 which in the one case consists in the outflow of many clear drops 

 from the egg, and in the other of one large drop. At bottom, 

 it only depends upon two modifications of the same process. 

 It may be mentioned that the result of the experiment remains 

 the same if 1 c.c. of 2J m NaCl is added to each 4 c.c. of propyl- 

 alcohol. 



5. We come now to a discussion of the cytolytic action of 

 distilled water. This type of cytolysis is of great importance 



