178 THE EVOLUnOM OF THE METAZOA 



We must again emphasize that old as well as the modern 

 embryologists who have studied the ontogeny of Anthozoa and 

 of scyphopolyps agree that sarcosepta (frequently these have 

 been less fortunately called mesenteries) develop by way of 

 a longitudinal folding of the intestinal wall. Kowalevsky (1873) 

 already had established this and he made fine illustrations of it. 

 Korschelt and Heider (1936:198) described this process in 

 their large 'Lehrbuch der Embryologie derAvertehrata, "Die Mesen- 

 terialsepten entstehen an der Wand als Langsfalten des Ento- 

 derms." In Actiniaria, as a rule, the first pair of sarcosepta which 

 shows a strictly bilaterally symmetric distribution develops 

 in this w^ay. L. Faurot (1913:283) is right when he speaks 

 of "deux plissements entodermiques." In scyphopolyps this 

 process has been described as a formation of the peripheral 

 pockets of the intestine; and this has actually the same mean- 

 ing. This formation of folds starts regularly closer to the oral 

 pole and develops in the direction of the lower end of the 

 body until it finally more or less disappears. 



Even if it is admitted by those who criticize the interpretation 

 which derives Anthozoa from Turbellaria that the sarcosepta 

 are a result of a longitudinal folding of the intestinal wall (e.g., 

 Luther in lit.), there still remains a great difference from the 

 conditions that can be found in Turbellaria. In theTurbellaria we 

 do not have, they state, septa or a longitudinal folding but ra- 

 ther the formation of intestinal diverticula. These are placed 

 transversally to the longitudinal axis of these animals and they 

 follow each other bilaterally. This objection is certainly true. 

 It is true that in the more or less flattened and bilaterally sym- 

 metrical Turbellaria the intestinal diverticula appear, as a rule, 

 as excrescences that are placed transversally to the longitudi- 

 nal axis of the animal, they are therefore on the right and on 

 the left sides of the intestinal tube, and not around the intestine 

 as this is the case with the cylindric Actiniae which stand erect. 

 If we tried to derive by all means (which would be certainly 

 wrong) one extreme case, an Actinia with its numerous partly 

 perfect and partly imperfect sarcosepta which appear in a bi- 



