570 THE POPULAR SCIENCE MONTHLY 



observed that the frog's egg may be made parthenogenetic by means of 

 a momentary electric shock. Unfertilized eggs of a frog were divided 

 into two equal lots, placed in distilled water, and one lot shocked elec- 

 trically. It was found that three times as much salt diffused out of the 

 shocked eggs as out of the control. Since the salt must have come from 

 the interior of the eggs, the experiment seems to prove that the eggs 

 must have been permeable to it. The shocked eggs began to segment 

 and behaved in other ways as if normally fertilized. 



There seems to.be no doubt that the permeability of the egg is in- 

 creased by agents producing parthenogenesis, but just how this influ- 

 ences the egg's development is not absolutely settled, because of the 

 many processes in development which are very far from being solved. 

 Some of these processes have been the subject of numerous investiga- 

 tions. The outward change in form during the segmentation of the 

 egg is caused by changes in surface tension. Granted that fertilization 

 alters the permeability of the egg, it may be that the changes in per- 

 meability influence the surface tension.* 



The unfertilized eggs of sea urchins, frogs and many other animals 

 are surrounded by jelly-like coats, the inner layer of which lies close to 

 the egg. On fertilization, the jelly is pushed out by the perivitelline 

 fluid exuding from the egg, the space occupied by the fluid being called 

 the perivitelline space. The inner layer of the jelly looks like a dis- 

 tinct membrane and is called the " fertilization membrane." Loeb con- 

 siders its formation of great importance. Biataszewicz has shown that 

 the frog's egg shrinks as this fluid is "secreted." Glaser has observed 

 the same phenomenon in the sea urchin's egg, though the shrinkage is 

 so slight that other observers deny its taking place. Granting that the 

 perivitelline fluid comes from the egg, the increase in permeability 

 would facilitate its migration. 



If the jelly be removed from the sea urchin's egg prior to fertiliza- 

 tion, no "fertilization membrane" appears. Presumably the fluid is 

 secreted but lost in the surrounding water.^ Though the membrane 

 helps to protect the embryo, its existence is not absolutely essential, 

 since eggs lacking it (due to the removal of the jelly) have been known 

 to develop. Many observations and experiments have demonstrated to 

 the writer that the tough " fertilization membrane " of the sea-urchin's 

 egg does not exist (at least in its final condition) before fertilization. 

 The increase in permeability allows the escape of the perivitelline fluid 

 which, according to the hypothesis advanced in 1911, interacts with the 

 jelly and forms the "fertilization membrane."® Elder, in 1913, came 



4McClendon, :Roux's ArcUv, 1913, 37, 233. 



5 McClendon, ' ' On the Nature and Formation of the Fertilization Mem- 

 brane," Internat. Zeit. f. Physik.-Chem. Biologic, 1914, Vol. 163. 

 ■ e McClendon, Science, 1912, 33, 387. 



