238 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



segmented, not only once, but many times. Why did they 

 stop developing? Surely not for lack of centrosomes, since 

 the fact that they segmented showed that they possessed them. 

 Our experiment therefore proves that the presence of astro- 

 spheres and centrosomes, and their ability to function, does not 

 guarantee the possibility of development. 1 



But it is not necessary to fertilize such eggs with sperm; 

 it suffices to induce membrane formation with butyric acid and 

 the}' will develop. The artificial membrane formation will have 



Fig. 73 Fig. 74 Fig. 75 



FIGS. 73, 74, and 75. Fertilization of blastomeres of an egg with sperm. The 

 blastomeres had been produced on the previous day by treating the egg with a 

 hypertonic solution. They had gone into a resting condition and upon the 

 addition of sperm formed a membrane and segmented regularly as the figures 

 indicate. Fig. 73 represents a dividing intact egg, while Figs. 74 and 75 originated 

 from a blastomere of eggs which had divided into two or four cells on the previous 

 day. 



this effect twenty-four hours or longer after the eggs have 

 been treated with the hypertonic solution. The membrane 

 fits rather tightly in this case. Hence eggs which had been 

 caused to develop by treating them for two and a half hours 

 with hypertonic sea-water and which had stopped segmenting 

 for twenty-four hours after reaching the two- or four-cell stage, 

 can be caused to segment regularly and develop into plutei if 

 they are treated with butyric acid 2 (Figs. 73-75) . 



This gives the impression that the stoppage of the develop- 

 ment after one or more cell divisions had been caused by the 



1 Loeb, "Die Superposition von kiinstlicher Parthenogenese und Samenbe- 

 fruchtung in demselben Ei," Archiv f. Entwicklungsmechanik, XXIII, 479, 1907. 



2 Loeb, Jour. Exper. ZooL, XV, 201, 1913. 



