ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 233 



couple of hours to hypertonic sea-water, i.e. sea-water to which had been 

 added sufficient salt and sugar to raise its concentration about GO p.c. 

 The developmental effect of the hypertonic solution increases with the 

 concentration of the hydroxyl-ions. Unfertilized eggs of Ghsetopterus 

 developed into larva? when Loeb added potassium and acids to the sea- 

 water, without it being necessary to increase the osmotic pressure. 

 Unfertilized eggs of starfish were made to develop by means of acids. 



When a spermatozoon enters an egg, a fertilization membrane is 

 formed. In 1905 Loeb discovered that a short exposure of the sea- 

 urchin egg to a monobasic fatty acid, or to C0 2 , led to the formation of 

 a typical fertilization membrane, and that a subsequent short exposure 

 to hypertonic sea-water resulted in development. Membrane formation 

 alone leads to segmentation, but disintegration may set in. The hyper- 

 tonic solution, with sufficient free oxygen, counteracts this. Another 

 counteractive was found in arresting development for two or three 

 hours, e.g. by putting the eggs in water without oxygen. Membrane 

 formation is the essential step in the activation of development, and 

 sometimes it is followed by normal larva?. 



A short exposure to cytolytic agents (such as saponin, solanin and 

 digitalin) induces membrane formation. In the case of Polynoe this 

 induces development of larva? ; in the case of StrongyJocentrotus the 

 eggs must be subsequently exposed to hypertonic sea-water in order to 

 counteract the injurious secondary effects of membrane formation. 

 Eaising the temperature may suffice to induce membrane formation. 

 Some eggs which are permeable to the " lysins " of foreign blood form 

 membranes and develop into larva?. The eggs of a marine mollusc, 

 Cumingia, sensitized with a solution of SrCl 2 , can be caused to develop 

 into larva? if treated with ox blood or serum. Extract of foreign cells 

 will also induce development. 



The spermatozoon seems to carry a cytolytic substance or " lysin," 

 which induces membrane formation, and another substance which 

 prevents disintegration. It may be that the slight parthenogenetic 

 tendency exhibited by many eggs depends upon the slight stability of 

 the emulsion at the surface of the eggs. It may be that the cytolytic 

 agents destroy the stability of the superficial emulsion. 



The artificial membrane formation may induce development by 

 accelerating oxidations. The entrance of the spermatozoon raises the 

 rate of oxidations from four to six times, the usual amount. This may 

 be due to an oxidase, or more probably to the change in the surface 

 layer. The entrance of two spermatozoa does not increase the rate of 

 segmentation. 



To preserve the life of the egg-cell in artificial parthenogenesis both 

 the membrane-forming factor and the corrective factor are necessary. 

 The oxidations going on in the mature but unfertilized egg are one of the 

 causes leading directly or indirectly to its death. It appears as if the 

 process of fertilization rendered the egg immune against oxidations, or, 

 in other words, transformed the egg from an anaerobe into an aerobe. 



Larva? reared from artificially parthenogenetic ova may be normal and 

 apparently healthy. Delage reared two sea-urchin larva? during sixteen 

 months to the stage of sexual maturity. Both were males. Loeb and 



