( 841 ) 



emplui.si/XMl llic })rol)loiH of tlie rclalioiisliip hchvcoii ('Iciiopliorii iiiid 

 Pltitheliiiiiitlis, l nieaii ('leiioplaiia and ('ocloplaiia. In (lilïcrciit degree 

 tliey unite [)ropei'ties of Uolli classes as has ali-eady heen elearlv eliu-i- 

 dated by their discoverers: Korotnki'f and Kowalkwsky. Yet iieitiier 

 Bourne who prepared llie Cteiiophora for Ray TjANKkstkk's h\i-ge 

 Textbook of Zoology, nor Kokschelt and Heider Iji tiicir handbook 

 mentioned above, nor Wit,t,kv, who lately studied Ctenoplana in a 

 livinu; condition, are reallv convinced of the |)Ossibilitv of a derivation 

 of Plathehninths from Ctenoi)hores, in -which case these two genera 

 shonld have to be considered as intermediate forms in that direction. 



So WiLLEY e.g. points out that it is jiot very })robable that littoral 

 forms would have sprung from pelagic ones, wliereas generally 

 the contrary is observed. This would according to him have been 

 a reversion of the natural sequence. The future will show, in 

 my opinion, that the difticidties mentioned, and raised by such able 

 experts, will for the greater part vanish as soon as relationships 

 "ao-ainst the srain", i. e. in the umiatural order, are no longer 

 accepted, but when both genera are considered as gradually' mutating 

 Plathelminths which are already fairly on the way of assuming 

 ctenophoran habitus. 



From what precedes we may at any rate infer that whereas the 

 Coelenterate relationship of the Ctenophora has faded, their com[)a- 

 rability with the Plathelminths has come to the fore. 



The data for judging in how far a derivation of the Annelids from 

 Plathelminths might be possible are given in extenso especially in 

 Lang's earlier and later i»ublications, more ])articularly in his well 

 known Gundapaper (1881) of which he has given an improved and 

 partly modified edition in his most recent essay, quoted in the 

 beginning. So I need only refer to this latest paper here. 



I for my part must now tiy to show that a derivation in the. 

 opposite direction presents no difficulties. We then should look upon 

 Plathelminths and Ctenophores no longer as ancestral forms but as 

 modified and in many respects unilaterally modified descendants of 

 a more primitive, Annelid-like type. 



Lang has already in his Polyclad-monograph (p. 674) openly 

 declared himself against such a view. Yet in the twenty years which 

 have since elapsed, various considerations have changed and it seems 

 that Caldwell's view (Proc, R. Soc. 1882 no. 222) has become 

 more probable again, according to which "there is a presumption . . . 

 that in fact Platyelminths are degenerate Enterocoeles." 



I should be willing like to undertake the defence of this thesis 

 and to see in the Plathelminths degenerate forms in which the 



