436 



EXPLANTING AND CULTIVATING 



Rudnick, on the other hand, by isolation culture methods on plasma clots, found that two 

 primary germ layers the ectoderm and endoderm seem to function more-or-less inde- 

 pendently, and that the notochord and axial mesodermal structures apparently depend on 

 the deginitive organization of the streak and node, or the head process, for realization 

 in vitro. Below is presented a figure from her paper showing the recognizable differen- 

 tiations from various regions of the early blastoderm when explanted in vitro. 



UED PLATE is t. 



SENS EP 



BODYiVALL 



MESENCHrKtE 



EPrTH soy. 



IMEDPLATEl 



HEART » 



MESENCHYME 

 EPYTH. 100'/, 



HEAKT i S^ 

 MID PLATE * 

 SENS EP 

 CHORDA f 

 BODY WALL 

 MESENCHYME 

 ERYTH SO'/a 



MED PLATE i SX 

 SENS EP 

 BODY tVALL 

 MESENCHYME 

 ERY TH ' 



MED PLATE 

 \HEART 



\heart soy, 



\ERYTH 100% 



MED PLATE SOV . 

 MESENCHYME 

 CHORDA' 

 HEART' 

 ERTTH 13 V. 



[ HEART 50 '/. 

 \tWTH. a'i 



Operating diagrams, showing structures differentioting 

 from each piece. Approximate percentages are given 

 in cases where they are thought of significance. 



From Rudnick 193S: Jour. Exp. Zool. 73:399. 



"Classifications are subjective concepts, nliicli have no absolute 

 demarcation in Nature, corresponding to tlieni .... Consequently, when 

 we attempt to define anything complex . . . we can scarcely ever avoid 

 including more ttian we intended, or leaving out something tliat should be 

 taken in. Thus it happens tliat on seefiing a definition of life, we have 

 great difficulty in finding one that is neither more nor less llian sufficient. " 



Herbert Spencer 



"The whole developnient of science, especially in recent years, is 

 a record of tearing down barriers between separate fields of knoivledge 

 and investigation. Little harm . and perliaps much gain, can come from 

 a frank avowal that we are unable to state clearly the difference between 

 living and non-living matter. This does not in any nay commit us to the 

 view that no such difference exists. " 



A. J. Lotka 



