836 



SCIENCE 



[N. S. Vol. XXXI. No. 804 



effort is unsuccessful and displays apparent lack 

 of accuracy in direction as well as distance of 

 height. Since the fish jump for the most part in 

 parallel lines perpendicular to the face of the 

 fall, one would expect to find some definite dis- 

 turbing influence to explain the apparently erratic 

 leaps. Such an influence is present in the con- 

 fused water currents at the base of the fall. The 

 sudden and irregular changes in the whirlpools 

 and swirls where the flsh lie waiting for an op- 

 portunity to jump no doubt act to modify the 

 direction of the leap and cause the fish at times 

 to execute apparently aimless jumps. The jump- 

 ing was most regular at the point where the cur- 

 rent was most constant. 



Reproduction and Parasitism in the Vnionidce-: 



Geoege Lefevbe and W. C. Cuetis, University 



of Missouri. 

 Further Experiments on the Egg-laying Habits 



of Amphitrite: John W. Scott, Kansas City 



High School. 

 Experiments on the Control of Asymmetry in the 



Development of the Serpulid, Hydroides dian- 



thus: Chaeij:s Zeient, University of Illinois. 

 A Statistical Study of the Sex-cells in the Early 



Stages of Amia and Lepidosteus : B. M. Au^en, 



University of Wisconsin. 

 Function of the Spermatozoon in Fertilinatio'n, 



from Observations on Nereis: Fbank R. LrLUE, 



"Lniversity of Chicago. 



The author succeeded in destroying the sperm 

 nucleus within the egg at stages as much as 

 twenty minutes apart shortly after the time of 

 its entrance, and found that while such eggs, 

 which had formed the fertilization membrane and 

 started in development, continued until the for- 

 mation of the second polar body, they did not 

 form a complete cleavage spindle and the egg 

 remained unsegmented. The female pronucleus of 

 such eggs formed the chromosomes but no definite 

 segmentation spindle, and asters were practically 

 absent. This was true even when one of the 

 maturation divisions had formed the polar nu- 

 cleus inside the egg, as sometimes happened, so 

 that the quantity of maternal chromatin equaled 

 that of the fertilized egg. It follows, therefore, 

 that fertilization is incomplete for some time 

 after the entrance of the spermatozoon into the 

 egg, in the ease of Nereis, and that its completion 

 is not merely a quantitative chromatin factor. 



The result was obtained by centrifuging eggs 

 at regular intervals from the moment of fertiliza- 

 tion on. There was found a sertaiu period soon 



after the entrance of the spermatozoon when the 

 mechanical shock destroyed the sperm nucleus in 

 large proportions of the eggs. This was deter- 

 mined by a cytological study of these eggs and 

 their controls in the maturation and fertilization 

 stages. The percentage of eggs thus studied and 

 found to be devoid of a sperm nucleus corre- 

 sponded quite accurately with the percentage of 

 eggs observed to remain unsegmented in the living 

 eggs of the same series. At the critical stage 

 selected for comparison, the determination of the 

 presence or absence of the sperm nucleus is a 

 simple matter. Stimulation of the unfertilized 

 egg with potassium chloride, or a mechanical 

 shook, will sufiice to cause the formation of the 

 fertilization membrane and of the polar bodies, 

 thus producing exactly the same efi'ect as the 

 first penetration of the spermatozoon, and no 

 more, for these eggs also did not segment. 



Fertilization can not, therefore, be regarded as 

 exclusively a surface phenomenon. It must be 

 interpreted as, in some sense, a continuous proc- 

 ess, lasting for some time after the penetration 

 of the spermatozoon, possibly until the union of 

 the germ nuclei. As one of the first efi'ects of 

 penetration is demonstrably increase of permea- 

 bility, it may be that the later function of the 

 spermatozoon is essentially similar throughout 

 the entire thickness of the protoplasm, by over- 

 coming, so to speak, a certain resistance to per- 

 meability in successive strata and creating a con- 

 sequent free oxidation in the interior of the egg. 

 The mass of the egg cell is obviously in excess of 

 the functional optimum for oxidation, and in- 

 creased permeability of only the surface would 

 hardly be expected to bring about free oxidation 

 throughout the whole. 



It is practically certain that the destruction 

 of the sperm nucleus by centrifuging did not 

 mean its expulsion from the egg in these experi- 

 ments, but merely suppression of its power of 

 growth, or dissipation of its substance. Its 

 material remains within the egg; but, existing 

 only as so much chemical matter, it does not 

 exercise a fertilizing effect. Its fertilizing power 

 is in some way bound up with its organization 

 and growth. 



The Chromosomes of Anasa tristis: C. E. Mc- 



Clung, University of Kansas. 

 Generic Definitions: C. C. Nutting, University 



of Iowa. 

 Some Parasites of the Sleeper Shark in Icy 



Straits, Alcska: Heney B. Wabd, University 



of Illinois. 



