694 



SCIENCE 



[N. S. Vol. XXX. No. 776 



course requires to be substantiated by a more 

 detailed study and I am making a cytological 

 investigation of the embryo sac development 

 and fertilization in 0. lata with the hope of 

 obtaining more conclusive evidence of the 

 presence of some form of apogamy in this 

 mutant. 



E. E. Gates 

 Missouri Botanical Garden, 

 September 29, 1909 



MEMBRANE FORMATION AND PIGMENT MIGRATION 



IN SEA URCHIN EGGS AS BEARING ON THE 



PROBLEM OF ARTIFICIAL 



PARTHENOGENESIS 



In a recent number of Science McOlendon' 

 has summarized his work on artificial par- 

 thenogenesis in Arhacia and discussed it with 

 reference to changes in permeability of the 

 surface layer of the egg. "With the same point 

 in view, during June and July at Tortugas 

 and the latter part of August, 1909, at Woods 

 Hole, I have been studying the earliest changes 

 taking place in developing sea urchin eggs, 

 especially the formation of the fertilization 

 membrane. 



Ever since the paper of Delage appeared, on 

 electric parthenogenesis, I have been impressed 

 with the great similarity in the means of stim- 

 ulating eggs to develop and the means of 

 stimulating muscles and sensitive plants. 

 Morgan expressed the situation clearly when 

 he compared the means of causing develop- 

 ment to a stimulus. A considerable mass of 

 evidence now exists, especially emphasized in 

 recent papers of Ealph Lillie, that stimula- 

 tion of muscles is effected by a momentary in- 

 crease in permeability of the muscle mem- 

 brane to COj, allowing its more ready escape 

 during contraction. C0„ is the chief end 

 product of the energy-yielding reaction on 

 which contraction depends and its removal 

 from the cells allows the reaction to proceed 

 (during contraction) to a new equilibrium 

 (of rest), when checked by a second accumu- 

 lation of CO,. The increase of permeability 

 on stimulation removes the condition which 

 is preventing the contraction. The move- 



' N. S., XXX., p. 454, October 1, 1909. 



ments of sensitive plants can best be ex- 

 plained as due to an increase in permeability 

 of the cell membranes relative to the turgor- 

 maintaining substances. The important point 

 is that processes in general brought about 

 by stimulation are connected with changes in 

 permeability. This holds good for secretion, 

 and the fact that the first visible change in 

 many eggs is a secretion is certainly signifi- 

 cant. 



Several authors have recorded instances of 

 development without membranes, perhaps the 

 best known case being parthenogenesis by 

 hypertonic sea water. I have repeated this 

 experiment and find that there is without 

 doubt a surface change in the egg, visible on 

 slightly high focus, which I take to be a mem- 

 brane very close to the egg surface. Similar 

 membranes are produced in Hippanoe eggs by 

 treatment with CH^COOH. They are hardly 

 noticeable even with the high power. Very 

 close fitting membranes and membranes which 

 surround each blastomere when the egg 

 divides may be produced in other ways. It 

 seems as if development without membranes 

 was rather a case of development without 

 pushing out of the membrane. 



This pushing out appears to be due to the 

 formation of some substance exerting an os- 

 motic pressure between it and the cell sur- 

 face, which absorbs the surrounding sea-water. 

 It would be impossible for the fluid between 

 fertilization membrane and egg to have come 

 from the egg without a greater diminution in 

 volume than is observed in eggs immediately 

 after fertilization. Loeb'' has discussed the 

 above view and designated a proteid or lipoid 

 as the substance in question. A very small 

 concentration of some substance formed just 

 behind the fertilization membrane would ac- 

 count for its pushing out, provided the mem- 

 brane were impermeable to the substance and 

 freely permeable to the salts of sea-water. 

 For the latter there is ample evidence. 



The membrane itself is a secretion com- 

 parable to the cellulose layers formed on 

 plant cells after division. It is composed 

 of some substance of a highly resistant nature 



'Arch. Entw. Meoh., XXVI., 1908, p. 82. 



