October 1, 1909] 



SCIENCE 



455 



following chemicals and conditions in sea- 

 water : acids, alkalis, hypertonicity, Lypotoni- 

 city, ether, greatly diminished oxygen, potas- 

 sium-cyanide, heat, cold, induction shocks and 

 mechanical agitation. In many cases the eggs 

 segmented while they remained in the artificial 

 solution. They would not segment in sea- 

 water charged with carbon dioxide unless most 

 of the gas were allowed to leave the sea-water. 

 They segmented in weak alkalis, hypertonic 

 sea-water, diminished oxygen, KCN and cold. 



From the above we may conclude that the 

 various parthenogenetic agents could not have 

 a similar chemical action and must have some 

 common physico-chemical action, most prob- 

 ably changing the permeability of the plasma 

 membrane, thus allowing the escape of carbon 

 dioxide (as suggested by Lillie). The fact 

 that eggs will not segment in concentrated 

 carbon-dioxide demonstrates the last point. 

 Lyon showed that the escape of carbon- 

 dioxide from sea-urchin eggs varied rhyth- 

 mically during cleavage, which suggests that 

 a period of increased permeability is necessary 

 for each cleavage. The stimulus to partheno- 

 genetic development need only be applied once 

 and the egg becomes automatic like any other 

 cell. 



The question arises whether these agents 

 have any additional efFect besides changing 

 the permeability of the membrane. When the 

 membrane becomes permeable some of the re- 

 agents must enter the cell. Probably this is the 

 reason that some reagents start development 

 that continues indefinitely, whereas after 

 others development soon ceases (the eggs being 

 injured by the reagent). Some chemicals may 

 cause an irreversible permeability that does 

 not initiate segmentation but causes death, but 

 these will not be considered. It seemed to me 

 that if the reagents caused a simple physical 

 change, one could be made to act as quickly 

 as another by finding the proper concentration, 

 and this I tried to do. Fifteen seconds' ex- 

 posure was suflicient with acetic acid while 

 about seventeen hours was necessary with 

 potassium cyanide. It is evident that the 

 actions of the two are different. Probably the 

 KCX slowly enters the egg while the mem- 

 brane is relatively impermeable and by re- 



tarding certain enzyme actions brings about 

 increased permeability of the membrane. Or 

 the KCN may make the membrane permeable 

 immediately and then enter the egg, retarding 

 the production of carbon-dioxide and thus 

 necessitating a longer period of permeability. 



Since the egg becomes automatic after one 

 of a number of stimuli the question arises 

 why it did not remain automatic like every 

 other cell in growing regions of the mother. 

 In studying the cell lineage of parasitic Cope- 

 pods I found that the germ cells could first 

 be distinguished from the soma cells by their 

 slow rate of division. In the thirty-tyco cell 

 stage, one cell is the primary germ cell and it 

 does not divide as soon as the other cells do, 

 but grows larger than they do. Probably its 

 failure to become sufficiently permeable to 

 divide as soon as the others allows it to grow 

 larger and become the germ cell. This may be 

 true of all its progeny and in the final genera- 

 tion, the primary oocytes, enormous growth 

 takes place and division is impossible without 

 a special stimulus. The plasma membrane 

 may not be sufficiently permeable for cell divi- 

 sion and yet allow the passage of nourish- 

 ment. Perhaps fats and lecithin may enter 

 the cell by dissolving in the lipoids of the 

 membrane. 



To sum up, we may conclude that all agents 

 initiating parthenogenetic development in the 

 egg of Arbacia cause increased permeability 

 of the plasma membrane, but some agents act 

 differently from others, either by having an 

 indirect action or by producing additional 

 effects. 



J. F. McClendon 



Woods Hole, JIass., 

 Aug. .31, 1909 



SOCIETIES AND ACADEMIES 



AMERICAN MATHEMATICAL SOCIETY 



The sixteenth summer meeting and sixth col- 

 loquium of tlie society were held at Princeton 

 University during tlie week September l.S to 18, 

 1909. Tlie four sessions of the summer meeting 

 proper occupied the first two days. Thirty-nine 

 members were in attendance. At the opening ses- 

 sion Professor Fine presided, being relieved at the 

 later sessions by Professor ilorley and Vice-presi- 

 dents Kasner and Van Vleck. The following new 



