176 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



in Fig. 43 there occurs an outflow of clear matter from the 

 cytoplasm, just as in membrane formation. This is quickly 

 followed by the clearing and swelling of the whole egg, until at 

 last it becomes a "shadow" (Figs. 44 and 45). The variations 

 that present themselves on examination of a quantity of eggs 

 in the saponin solution occur principally in the membrane 

 formation. In many cases the formation of vesicles, which is 

 here depicted in Figs. 40 and 41, did not take place. Instead 

 of this, the egg proceeds from the stage drawn in Fig. 39 directly 

 into the stage of membrane formation (Fig. 42). As an inter- 

 mediate stage one observes cases in which only a roughening 

 of the surface of the egg takes place, owing to the formation 

 of numerous minute drops, which suddenly swell simultaneously 

 and give rise to the formation of the surface membrane; at first 

 this is closely adjacent to the cytoplasm, but as a result of the 

 osmotic pressure more sea-water is always flowing in, until the 

 tension of the membrane counterbalances the osmotic pressure. 

 The examination of these drawings also gives the impres- 

 sion that the effect of the saponin is produced in two distinct 

 stages, which do not necessarily merge continuously into each 

 other; the first stage is probably the effect upon the surface of 

 the egg, leading to membrane formation, and the second is 

 obviously an effect produced upon the interior of the egg, and 

 leads to cytolysis. In both cases the liquefaction is associated 

 with a swelling and increase in volume. 



When eggs that have been treated with saponin until 

 membrane formation has taken place are freed from the last 

 trace of saponin by washing them four to six times in pure 

 sea-water, they behave just like eggs in which the artificial 

 membrane has been produced by a fatty acid. If they are left 

 in sea-water, development starts, and the stage to which they 

 develop depends on the temperature. If they are subsequently 

 treated for about forty minutes (at 15 C.) with hypertonic 

 sea-water, they develop into larvae. 



