306 ME. J. E. DUEEDEN OW 



the coelomic spaces are formed. To continue the comparison 

 with the Tripoblastica, may we not regard it as the equivalent of 

 'the " mesenchyme " of the higher Metazoa ? It is evident that 

 in LehrMnia it is little more than a larval " packing-tissue," 

 disappearing as the adult Scyphozoan characteristics are taken 

 on. As already mentioned, however, it probably shares in the 

 formation of tbe muscular system. 



Even though beyond the oesophagus no separate digestive tract 

 with closed walls remains in the adult, there seems little doubt 

 that the mesenterial filaments are to be looked upon as repre- 

 senting an endodermal-lined digestive gut, continuity with the 

 oesophagus being either original or established at a very early 

 stage. As the primary distinctness of the coelomic pouches has 

 broken down at an exceptionally early stage, so the walls of the 

 enteron come to be represented only by thickened ridges along 

 the free edge of the septa of the coelome. Or the same result 

 may thus be conversely stated, and pei'haps with greater morpho- 

 logical truth, that as the lower portion of the enteron beyond the 

 point at which diverticula are given off is not formed early 

 enough, so the mesenchyme and coelomic epithelia, which on 

 •their part are developed and would have surrounded it, become 

 disintegrated, leading to the imperfect condition of the coelomic 

 chambers in the adult. It only remains to conceive of the adult 

 mesenteries uniting along their lateral edges and we should 

 have a closed gut as in the higher Metazoa, lined above by the 

 invaginated ectoderm and below by the archenteric endoderm. 

 The mesenterial chambers thus distinct from one another would 

 constitute a true coelome or body-cavity, exactly as in the oeso- 

 phageal region and in tbe Enterocoela. As it is, the Scyphozoa 

 are distinguished by having the lower portion of the enteric 

 system in separate longitudinal bands, its cavity in communication 

 laterally and below with the chambered body-cavity. 



"Were the explanations here offered to be confirmed, the occur- 

 rence in the Scyphozoa of an archenteron with distinct radiating 

 coeloraic diverticula would be recorded for the first time, but the 

 hroad relationships of the group with the higher Metazoa thereby 

 implied have been already surmised by various workers. 



Prof. E. B. Wilson (1884), in his paper on " The Mesenterial 

 Eilaments of the Alcyonaria," devotes a section to the relations 



