COELENTERATA. 



107 



FIG. 92. Eight-armed Scyphistoma-polyp with 

 wide mouth. M longitudinal muscles of the 

 gastral ridges; Csk chitinous tube. 



a strictly radiate and 

 a bilateral structure. 

 The tentacles rarely 

 show a tendency to 

 the bilateral arrange- 

 ment, but the mesen- 

 teries, as shown 

 by the arrange- 

 ment of the lon- 

 gitudinal muscu- 

 lar bands, are 

 generally grouped 

 in a bilateral 

 manner (Figs. 88 

 and 89). 



The Scypho- 

 polyp or Scy- 

 phistoma is a 

 transitional form 

 between the 

 Hydro- and An- 

 thozoan- polyp. 

 It resembles the 

 hydroid in the 



and the horny corals (Anti- 

 patliarioi) their 6-radiate sym- 

 metry by their six tentacles; 

 multiradiate usually in ^ mul- 

 tiple of six are the Actiniaria 

 and stone-corals. Nevertheless, 

 hardly a single anthozoan-polyp 

 can be found in which all the 

 organs are strictly arranged 

 according to one and the same 

 number. The fact that the 

 mouth-opening is not usually 

 round, but slit-like, indicates 

 an inclination to a biradiate or 

 bilateral symmetry, and there 

 are transitional forms between 



FIG. 93. Sixteen-armed Scy- 



; phistoma (slightly |magni- 



fied). GttTgastralJridges. 



