INITIATION OF DEVELOPMENT IN EGG OF ARBACIA.' 409 



changes induced by sperm are not merely quantitatively but quali- 

 tatively different from those induced by hypertonic sea-water ; the 

 cortex is liquified following insemination with resulting membrane 

 separation, but it is thickened by hypertonic sea-water. If any- 

 thing were wanting to substantiate the view here presented, Heil- 

 brunn's own findings would do so : many diverse agents besides 

 hypertonic sea-water produce coagulation in the egg. That Heil- 

 brunn does not show that all of these so-called agents of artificial 

 parthenogenesis do actually produce cell division and this accord- 

 ing to his own definition of artificial parthenogenesis they should 

 do alone is fatal for the whole theory. In addition, it is not 

 beyond the realm of possibility that many of these agents (distilled 

 water acting upward to four minutes, toluene acting for five min- 

 utes, saponin acting for five minutes, etc.) simply induce death 

 changes of no significance whatsoever for the problem of fertili- 

 zation. 



There remains the fertilizin theory (Lillie, '14). Here we find 

 no difficulty. Eggs of Arbacia following exposure to hypertonic 

 sea-water possess fertilizin despite mitotic changes. Such eggs on 

 insemination, as we should expect, give complete cortical reaction. 

 Without insemination such eggs develop. Fertilizin fertilises the 

 sperm so that it may by reacting with aster-forming substance of 

 the egg start up division in which the egg nucleus takes part. But 

 eggs that are already induced to develop by hypertonic sea-water 

 do so through localization of aster-forming substance around their 

 nuclei. Sperm entering such eggs may still react with fertilizin, 

 thereby setting free cortical changes leading to membrane sep- 

 aration. 



LITERATURE. 

 Chambers, R. 



'17 Microdissection Studies, II. The Cell Aster: a reversible Gelation 



Phenomena. Jour. E.vp. Zool., XXXIII., 483-504. 

 Conklin, E. G. 



'17 Effects of Centrifugal Force on the Structure and Development of the 



Eggs of Crepidula. Jour. E.vp. Zoo!., XXII., 311-420. 

 Heilbrunn, L. V. 



'15 Studies in Artificial Parthenogenesis. II. Physical Changes in the Egg 

 of Arbacia. BIOL. BULL., XXIX., 149-203. 



Lillie, F. R. 



'06 Observations and Experiments Concerning the Elementary Phenomena 



