296 THE EVOLUTION OF THE METAZOA 



treating the spermatozoa of the Eumetazoa in a similar 

 way to the spermatozoa of these aberrant species, and when he 

 states, "This is a pure conjecture with no basis in facts, but 

 necessary for Hadzi's view" (Jagersten, 1959 : 93). 



I refuse to accept this accusation because it is completely 

 unjust; at the same time I wish to emphasize that even if 

 there were no case of Entodiniomorpha, my interpretation 

 would still appear as more probable than the interpretation 

 which was proposed by Jagersten, especially in those cases 

 where he refers to the excellent research that was done by 

 Ake Franzen (1956). The form, the structure of the spermato- 

 zoa, and the spermatiogenesis are so widely different not only 

 when w^e compare different animal groups but also wdthin 

 the frame of one and the same systematic unit; we are there- 

 fore completely unable to develop on this basis a clear idea 

 of the phylogeny of animals and we can also oppose on this 

 basis a derivation of the Eumetazoa from some infusorial 

 ancestors. It should suffice if we quote here the statement 

 inade by Franzen (1956 : 467) in the summary to his w^ork; 

 here he states that the spermatozoa of a "primitive type" 

 can be found in such numerous and widely different animal 

 groups as are, '^Cnidaria^ Plathelminthes (onljXenotlmrbella bocki.), 

 Nemertini, Aschelminthes (only Priapuloidea), Annelida, 

 Echiuroidea, Sipunculoidea, Mollusca, Tentaculata (only 

 Brachiopoda), Echinodermata, Enteropneusta, Tunicata, and 

 Acrania." 



It should not be taken too tragically that the spermatozoa 

 of the Acoela do not belong to this primitive type. In the 

 Acoela the spermatozoa had been able further to develop 

 equally one-sidedly as their organs of copulation. In these 

 and in their hermaphroditism they differ from the Nemertinea 

 which have also reached a low level of evolution. The internal 

 insemination and fertilization, which w^e believe that the Tur- 

 bellaria had inherited from their infusorial ancestors, has been 

 preserved in the side line of Platyhelminthes only (Trematoda, 

 Cestoda). In numerous other side-lines of evolution, however. 



