130 REPORTS ON INVESTIGATIONS AND PROJECTS. 



and unfertilized, to change from red to yellow, that 5 minutes after fertiliza- 

 tion the egg is more permeable to alkali despite the fact that it is surrounded 

 by a fertilization membrane. The same is true if we form the membrane 

 artificially with acetic acid. In the only series of experiments performed, 

 with Toxopneustes eggs, between 10 and 15 minutes after fertilization the 

 eggs returned to practically the same condition of permeability as the unfer- 

 tilized eggs. There appears to be a second increase at the time of first 

 cleavage. 



Tennent had discovered in 1909 that the sperm of Holothuria tubcrosa had 

 a very destructive action when added to the eggs of Toxopneustes. A rather 

 thick, close-fitting membrane is formed, which fails to push out, while the 

 egg shrinks irregularly. If the sea-water is now made hyperalkaline (100 c.c. 

 sea-water -f- 1.2 c.c. N/10 NaOH) the alkali enters stained eggs, turning the 

 neutral red into yellow, and soon the egg swells. This suggests that the 

 sperm of Holothuria contains a lysin (Loeb) which enormously increases the 

 permeability of the egg of Toxopneustes to alkali and which eventually leads 

 to cytolysis. 



Attempts to find a stain which will enter eggs and be changed in color by 

 acids, or an egg occurring at Tortugas and containing a natural pigment 

 affected by acids, have thus far been in vain. 



CYTOEYSIS. 



The problem of cytolysis, as intimately connected with that of membrane 

 formation, was also studied. The two most important phenomena connected 

 with cytolysis in sea-urchin eggs are : swelling of the egg and decomposition 

 of the visible granules, which appear to fuse to larger and more liquid 

 spheres, with a loss of their natural pigment or of their stain if they have 

 first been placed in a solution of neutral red. 



By centrifuging and then cytolysing (with chloroform or saponin), or 

 cytolysing and then centrifuging, it was possible to determine that of the 

 three granular substances present only the yolk and pigment granules break 

 down. The oil is unaffected. Swelling and disintegration of the granules 

 take place simultaneously. It is impossible to say which precedes and which 

 follows. Many eggs (e. g., Spirobranchus) contain granules which do not 

 break down on cytolysis, yet the eggs swell, so that it would appear as if the 

 connection of the granules in an egg with cytolysis were purely secondary, 

 and that saponin or chloroform do not combine with them and break them 

 up. This supposition is further supported by the fact that the granules (ex- 

 cepting oil) of sea-urchins' eggs are broken up into exactly the same products 

 characteristic of cytolysis zvhen the eggs are crushed in sea-water. This can 

 only mean that the conditions for stability of the granules in the egg are very 

 different from those in sea-water ; that there is something in the egg in whose 

 presence the granules are stable, which is not in sea-water, or vice versa, and 

 that the egg-surface forms an impenetrable barrier for this substance, in so 

 far as simple diffusion is concerned. 



It has since been found that calcium salts are the substance in the presence 

 of which the yolk granules are unstable, and that a mere trace is all that is 

 necessary to cause granular disintegration. If cytolyzed in pure 0.6 molecu- 

 lar NaCl the granules remain intact, although they are changed in some way, 

 for any dye or pigment they may contain passes out of them. The egg 

 nevertheless swells. The cytolysis of the sea-urchin egg would be in all re- 

 spects like that of the annelid were it not for the calcium of the sea-water. 

 The yolk granules of the annelid egg do not break down in sea-water. The 



