176 THE EVOLUTION OF THE METAZOA 



sarcosepta that occur in scypho- and anthopolyps as longitudi- 

 nal folds of the "D^r////?/^//" (intestinal layer) is not so frequent; 

 it was made, by Grobben and Kiihn in the well known 

 Lebrh/cb derZoo/ogie (1932:461), "DieSepten. . . sind senkrechte 

 von der Seitenwand, der Fuss- und Mundscheibe entspringen- 

 den Falten des Darmes. . ." A. Kastner, in the recent ''Lehr- 

 huch der spe^^iellen Zoologie,^"* avoids defining the sarcosepta 

 of Anthozoa; he mentions, however, in connection with scy- 

 phopolyps, four folds of the entodermal wall which are direct- 

 ed centralwards (1954:109). Hyman, in her Manual of the 

 Zoology of Jnvertebrata (1954:367), tries to combine the two 

 standpoints and writes as follows, "Primitively consisting of 

 a simple tube, the digestive system displays through the phy- 

 lum a tendency to complication by putting out branches and 

 pockets and in the Scyphozoa and Anthozoa is divided into 

 compartments by gastrodermal-mesogloeal projections." 



The septa of scyphopolyps (earlier they were frequently 

 called taeniolae) were previously considered by zoologists 

 as homologous to the sarcosepta of Anthozoa; these were 

 previously called mesenteries, in spite of the fact that 

 the conditions that can be found in scyphopolyps give 

 the impression of longitudinal folds which are developed due 

 to the formation of peripheral sacks. On the other hand, there 

 was nobody who thought of a possible homology of these 

 septa, together with the intestinal pockets that occur between 

 them, with the intestinal diverticula of Turbellaria. It was con- 

 sidered that the two forms had been developed quite inde- 

 pendently from each other. There is not yet a distinct intestinal 

 tube in Acoela, in Rhabdocoela this tube is smooth, approxi- 

 mately as it is in hydropolyps, and it is only in the "higher" 

 Turbellaria (Polycladida, Tricladida, etc., according to the old 

 system) that, a gastrovascular system has been developed which 

 becomes increasingly complex, w^hose ramifications can finally 

 develop into a whole net, similar to that observed in some 

 Ctenophora. It was therefore quite impossible to believe 

 that Cnidaria could be deduced from Turbellaria, or vice versa. 



