PREVIOUS INTERPRETATIONS OF CNIDARIA 169 



Quite generally we can reconstruct the history of the pha- 

 ryngeal tube as follows. The primitive Turbellaria (there are 

 such species even among the recent Turbellaria) do not yet 

 possess a constantly developed pharynx. Palmenia has, accord- 

 ing to Bresslau (1909), an oral opening in its surface through 

 which the animal can stretch its digestive plasmodium (a real 

 intestine has not yet been developed) in order to pick up 

 particles of food. There is no reason to doubt that these are 

 really the primitive conditions which had been inherited by the 

 acoelous Turbellaria from their supposed infusorial ancestors. 

 During the next higher stage in the evolution of Turbellaria, 

 the invagination of the skin at the oral opening took place 

 —with simultaneous active locomotion and macrophagia — 

 this development took place also as early as in Infusoria; it 

 led afterw^ards to the development of a special protrusile 

 pharynx. The ability to form a gullet tube had been inherited 

 by Cnidaria, that is specifically the Anthozoa, from their 

 turbellarian ancestors. We are unable to determine the rela- 

 tionship between the structure of the present-day Anthozoan 

 pharynx, the primitive Anthozoan pharynx, and the primi- 

 tive Turbellarian pharynx. The pharynx had anyhow been 

 developed in the Anthozoa in a progressive and independent di- 

 rection, and that in connection with the evolution of the septal 

 apparatus. Even if there are at present whole families among 

 the recent primitive rhabdocoelous Turbellaria which have a 

 pharynx simplex (e.g. Catenulidae, Microstomidae), this does 

 not necessarily mean that the turbellarian ancestors of Antho- 

 zoa had only a pharynx simplex. The possibility must also be 

 taken into consideration that at best the present state could be 

 a result of a retrogressive development, especially in view of 

 the fact that the sessile way of life leads to a reduction of the 

 general organization. 



In the Anthozoa a diversity can be observed in the subse- 

 quent destiny of their gullet tube (pharynx) ; whether it occurs 

 in solitary species which are capable, however slightly, of lo- 

 comotion, or in species which form cormi and which are 



