Septesxbee 26, 1913] 



SCIENCE 



449 



No membranes appear in the controls, nor do 

 the eggs whose membranes have appeared de- 

 velop when returned to sea water. Three 

 possibilities suggest themselves — an acid ef- 

 fect, a mechanical eiiect or a heat effect. No 

 decisive experiment has as yet been devised. 



These experiments suggest that in Arhacia 

 punctulata the membrane swells before the 

 sperm enters the egg, and not after. Experi- 

 ments also show that when the phase boundary 

 between Kite's jelly and the outer jelly is 

 complete, sperm do not readily penetrate the 

 fertilization membrane. From this it follows 

 that the penetration occurs at the moment 

 when the jelly is softened and begins to swell. 

 Accordingly, eggs whose jelly has been par- 

 tially softened by heat or infusoria should be 

 capable of fertilization with small doses of 

 sperm. This has actually been observed in a 

 number of instances. The opposite exijeri- 

 ment of hardening the jelly with Ca has been 

 performed. Such eggs are extremely difficult 

 and in many cases impossible to fertilize as 

 the sperm do not stick. 



VI. THE RELATION BETWEEN FERTILIZATION AND 

 THE FERTILIZATION MEMBRANE 



The relation between the initiation of devel- 

 opment and the fertilization membrane in 

 Arhacia punctulata is one of association 

 rather than " causal," for the membrane may 

 be made to appear without development, and 

 development may be initiated without the 

 appearance of the membrane. In Asterias 

 forhesii the association is somewhat different, 

 and so intimate that any method which causes 

 the membrane to appear is at the same time a 

 method of initiation provided the violence 

 is not too great and the egg is in good condi- 

 tion and in a suitable medium. The explana- 

 tion is simple. In Asterias the fertilization 

 membrane does not depend on the swelling of 

 a formed jelly, but instead, the egg peels itself 

 away from the inner surface of a thin pre- 

 existing membrane. This peeling away seems 

 to depend, not upon changes in the fertiliza- 

 tion membrane, but upon changes in the sur- 

 face film of the egg. When this is rendered 

 more permeable, material leaves the egg and 



the egg shrinks away from its closely adherent 

 covering which thus becomes visible. The 

 perivitelline space in the starfish egg is homol- 

 ogous with that of the sea urchin egg, but is 

 much larger. 



The type of fertilization membrane found 

 in Arhacia punctulata may be called hydro- 

 philous, that of the starfish, Asterias forhesii, 

 anhydrophilous. 



VII. ON THE LOSS OP SUBSTANCES BY THE EGG 

 AND THEIR NATURE 



The starfish egg upon peeling off from its 

 anhydrophilous fertilization' membrane is 

 markedly smaller in volume than before. The 

 same thing is true of Arhacia. Exact meas- 

 urements will be given when I publish exact 

 details of these experiments. No doubt much 

 of the material lost by the egg is water. F. E. 

 Lillie* in a series of fundamental researches 

 has shown that the fluid over-fertilized eggs 

 may contain at the least two classes of sub- 

 stances, (o) " iso-agglutinins " and (h) a sub- 

 stance having a chemotactic influence on the 

 sperm. From Elder's' investigations as well 

 as certain observations of my own, it appears 

 possible that the chemotactic substance is con- 

 tained in the outer jelly of the Arhacia egg. 

 I have been able to verify the " iso-agglutinin " 

 and its effects as described by Lillie in the 

 case of Arhacia and Asterias. 



Ovarian extract of Arhacia, when present in 

 sufficient quantities, retards the development 

 of normally fertilized Arhacia eggs. If the 

 extract is added to blastulae which have de- 

 veloped in normal sea water, these are instantly 

 slowed dovm and absorb water. Arenicola 

 larvae also have their permeability increased 

 by the Arhacia extract, as can be very prettily 

 seen by their loss of pigment. They also slow 

 down in their movements and are slightly and 

 reversibly agglutinated. 



■* Lillie, IF. E., ' ' Studies of Fertilization, ' ' I. 

 and II., Jour, of Morph., Vol. 22; III. and IV., 

 Jour, of Exp. Zool., Vol. 12; V., Jour, of Exp. 

 Zool., Vol. 14. 



= Elder, J. C, "The Eelation of the Zona Pel- 

 lueida to the Formation of the Fertilization Mem- 

 brane, " Arch. f. EntwicTclwngsmechanih, Vol. 36. 



