316 THE EVOLUTION OF THE META20A 



syncytia; any experiments in this connection are completely 

 superfluous. This is a phenomenon which can be found 

 scattered in the whole animal world, a fact which has been 

 recognized long ago. We even know that among algae 

 which have reached a low level only in their organization 

 (they are therefore certainly primitive organisms among the 

 polycellular forms) there is a whole group, among the Siphon- 

 ales, which shows a strong inclination to form syncytia, in 

 spite of the fact that these are plants and thus colonial poly- 

 cellular forms whose cells had evolved quite generally strong 

 membranes. In the best known case, in Caulerpa, we find 

 cellularity eliminated to such a degree that it appears only 

 slightly during the phase of the formation of gonads while 

 at the same time it has completely disappeared from the onto- 

 geny. In spite of this Caukrpa has remained a lowly organized 

 alga, and therefore a plant. 



We are particularly interested in the cases that were 

 observed by Reisinger during his experiments where a cellular 

 state was developed from a syncytial (plasmodial) state. It 

 should be mentioned in this connection that a trend must 

 be taken into consideration by means of which the cellular 

 tissue of the Eumetazoa developed from the plasmodia. 

 Moreover, it is quite difficult, even if not impossible, to 

 decide precisely whether in a given case wx have a true 

 primary plasmodium or a secondary syncytium. In the case 

 of the more highly developed Turbellaria it must also be 

 taken into consideration that their plasmodia have already 

 reached a state of readiness to pass over into a cellular state ; 

 in these a slightly stronger irritation can be sufficient to pro- 

 duce a segregation of their karyons, and thus the formation 

 of cells. Reisinger did not quote any example of artificial cellu- 

 larization of the plasmodia Acoela. 



As a contrast to all this we can find the very instructive 

 experiments that were made by Steinbock in the most 

 primitive Acoela (Amphiscolops) . Steinb5ck could prove with 

 these experiments that all three parts of the archhiston, all 



