CNIDARIA 



111 



owever, the four tentacles that immediately succeed the four primary 

 ones are not placed over the septa, but bud out from the corners of the 

 gastral pouches of the second pair, which lie next to the septa, and only 

 gradually move into positions over the septa. In this way, their axial, 

 entodermal cords acquire connections with the gastral pouches of the 

 second pair. Since the gastral pouches of the first pair soon follow with 

 the formation of four new tentacles, the equivalence of the first four 



Fig. 54. — Diagrammatic representation of the structure of an older Scjpbistoma 

 (based upon Gobtte, from Hatschek's Lehrbuch). A, longitudinal section : at 

 the left, perradial; at the right, interradial ; AB, chief axis; o, mouth ; s, inner 

 opening of the oesophagus; gt, gastral pouches; gr, gastral furrow; so, septal 

 ostium ; tr, septal funnel ; sm, septal muscle (the dotted line does not quite reach 

 to it) ; B, transverse section through the lower part of the body ; gr, gastral fur- 

 row; 8, septum ; sm, septal muscle; C, view of the oral side (references as in A). 



primary gastral pouches is established for the first time in the stage with 

 twelve arms. Goette, therefore, maintains that the numerical series, 4, 

 12, 20, 28, etc., is the primitive one for the budding of the tentacles, 

 whereas the actually observed series, 4, 8, 16, 24, 32, etc., corresponds to 

 a coenogenetically modified condition. It should be mentioned that the 

 formation of each new tentacle takes place by an outfolding of the cor- 

 responding part of the gastral pouch, so that in reality a small secondary 

 gastral pouch is produced with every tentacle. 



