THEORY OF MEMBRANE ELEVATION. 2J9 



It should perhaps be pointed out that in cases of extreme 

 coagulation of the protoplasm, the contents of the egg may some- 

 times be made to shrink a\\ ay from the vitelline membrane. Xo 

 good case of this is known for the sea-urchin egg, although some 

 shrinkage apparently occurs after prolonged heat coagulation. 

 In the Cnmingia egg. which has a much stiffer membrane than the 

 sea-urchin egg, a membra IK- which does not normally become 

 elevated, some 191- rimeiits showed that the protopla-m 



would -brink away tn>in the \itelline membrane when the e.u.u 

 (ontent- had been t lion m^hly coagulated after -r\eral hour-* 

 e\po-ure to h\ pertonic -olut i< >n-. Such slow < o.i-ul.tti\ e -hrink- 

 el\ to be confused with true nu-mbrane elevation, 

 although in the ('until:, g under certain conditions the mem- 



bi.tiie may bei oin- d away from the I'ter it i- 



released. 



Ju-t make- one oi her point against the surface ten-ion theory. 

 Il- ~i. ii<- ih.u in "tin -if Arbacia and Echiinirachniit* any 



* oiii]eient observer car see thai membrane separation following 

 insemination i- no mere -miare tension effect." Thi- i- not a 

 \.i\ -ciiou- .dxumeiit . The surface tension theor) claim- only 

 that the lowered surl ;ion is the cause which. underlies the 



pro, ess, not tint all the dri.iil- which follow the initiation , ,t t he 

 trii-ion phenomena. A; \\.iyhowi.m 



one decide a physical problem by mere visual obsen at ion? 



Jll-l, ap|areiltl\-, ha- attempted to do thi.-. The lifting >M "t" 

 the membrane i- a physical pmce and demand- a ph\>ical 

 explanation. |i ,-h to thi- i- hi- de-rripiion 



of membrane elevation a- in\ol\in^ a "wave of negativity" (9). 

 Hut he doe- not ti-e the \\-i -rd in any known phy-ical -en 



ki I I ki NI i 



i. Heilbrunn. 

 '13 BIOL. BULL., XXIV., 15. ib.. XXIX.. i 



. Traube. 



'09 Biivli.-m. /,-it-. li.. X\ '[.. i 



3. Godlewski. 



Winterstein'a Handbuch dei \.-n;lrKh.-ii.l.-n I'lr. : 



4. Garrey. 



'19 Hi.u . Hi i i ... XXXVII . 287. 



5. Moore, A. R. 



'12 t'niv. ni ( alitomi.i I'ul.lu atiuns in IMiysiolojjy. I\'.. 



