PREVIOUS INTERPRETATIONS OF CNIDARIA 117 



been preserved here; these have lost their independent cha- 

 racter, yet they have become specifically differentiated, and 

 they have been wholly preserved in the active parts of polyps. 

 These layers, have disappeared in the impersonal colonial 

 parts (solenia, caulus, rhiza). It is only among the pelagic 

 individualized cormi of the Siphonophora with their well 

 developed hydrocauli (hydrosomes) that the layer with 

 muscles can be found well developed even in the impersonal 

 parts, a fact which can be easily understood. 



Several remains of an internal muscle system have been 

 preserved in the anthopolyps of the solitary Actiniaria. These 

 are the basally situated transversal muscles which are active 

 when the animal creeps for\vard; a whole system of the so- 

 called septal muscles that occur in sarcosepta and whose fibres 

 are placed longitudinally because they function as retractors; 

 and, finally, the circular muscles that can be found close to 

 the oral disc and which function as an oral sphincter. Here, it 

 becomes clear how little it corresponds to the facts, if we speak 

 about entodermal or ectodermal muscles for the sole reason 

 that sometimes these muscular fibres appear to be more 

 closely connected with the skin epithelium, another time with 

 the intestinal epitheUum, and as the third possibility they be- 

 come independent because they had been separated from these 

 epithelia. Scholars of the old school have frequently run into 

 difficulties when they have tried to decide to which of the two 

 body layers (either ectoderm or entoderm) they should have 

 attributed a certain group of muscular fibres. Yet, as a matter 

 of fact, all these muscular fibres belong to the middle layer 

 only, regardless whether we call this third middle layer a me- 

 sogloea, mesoderm, mesoblast, mesenchyme, or, as I have 

 called it, a mesohyl; it is always one and the same part of 

 the body. 



In the Scyphozoa, the polyps have inherited as their inner 

 muscles from their anthozoan ancestors the poorly preserved 

 taeniolan bundles of muscles. There are, with few exceptions 

 ( Naiisitho'e-Stephanoscjphm) , four such retractors which used 

 9 



