THE FERTILIZATION-REACTION 



urchins are rendered highly susceptible to poly-sperm-entry 

 whilst their ectoplasm becomes thickened and the mem- 

 brane only slightly separated. The same result obtains 

 after exposing the eggs to the alkaloids, strychnine, nicotine, 

 etc., as the Hertwigs^ showed in their now classic experi- 

 ments. If one repeats their observations one marks the 

 striking responses of the egg-surface to insemination, among 

 others, the longer duration of the many "fertilization- 

 cones." The ectoplasm need not be severely injured in 

 order that polyspermy succeeds. If the ectoplasmic 

 response to insemination be slowed down, polyspermy may 

 ensue. Thus, if one knows that eggs of a given lot are 

 below normal by having learned through trial insemina- 

 tions on some of them that the surface-changes underlying 

 membrane-separation proceed at an abnorrrially slow rate, 

 one can by inseminating with a heavier sperm-suspension 

 than that usually employed secure polyspermy. 



Some animal eggs, as those of cartilaginous fishes, of some 

 amphibians and of birds, are normally polyspermic. Poly- 

 spermy has also been reported in insect eggs. All normally 

 polyspermic eggs are large. ^ But since there exist also 

 some large eggs which are not polyspermic, it is, presum- 

 ably, not so much the size of the Qgg but the slow reaction 

 of its ectoplasm which makes polyspermy possible. 



The suddenly arising fertilizable condition of animal eggs 

 thus resides in the ectoplasm. The indications are that 

 this is a chemical reaction. Consider the problem of spe- 



1 Hertwig, 0. and R., 1SS7. 



~ Bonnevie^s conclusion {igoy) that polyspermy obtains in eggs of 

 Membranipora is incorrect as careful study of her paper reveals. 

 See also my failure to find polyspermy in this egg — Just, 1934. 

 MacBride'' s statement that polyspermy occurs in eggs of Pedicellina 

 is undoubtedly due to his error in interpreting Hatschek^ s statement 

 that he often observed numerous 7notile spermatozoa in the perivitelline 

 space. 



203 



