THE EDWARDSIA-STAGB OF LEBEUNTA. 293 



already developed below. This is clearly shown in fig. 22, 

 representing the centripetal, swollen portion o£ the sulco-lateral 

 pair of mesenteries of an extruded larva of intermediate age. 

 The section is taken transversely a little below the gullet. At 

 this level the mesentery to the left presents the beginnings of a 

 filament at its free edge, easily distinguished by the oval, 

 deeply-staining, closely-arranged nuclei and fringe of cilia ; the 

 mesentery to the right possesses only unmodified epithelium. 

 Only a few sections lower, however, the filament begins to appear 

 on the right mesentery also, and still lower is nearly as strongly 

 developed on both, as shown in fig. 19, taken from a non-extruded 

 larva. Such a separation between the filaments and oesophageal 

 lining occurs in several larvae of which I possess transverse 

 sections, and also in one longitudinal series. 



Any hiatus, however, is of a very temporary character. For 

 in other early stages the filamental tissue already starts directly 

 from the point at which the mesentery severs its connection with 

 the oesophagus, at first very feebly developed, but becoming 

 stronger below. Later, it is fully developed along the whole of 

 its extent. 



In this connection the outward and upward continuation of 

 the archenteric or oesophageal lining which takes place at the 

 fiboral termination of the oesophagus must be referred to (figs. 17, 

 18, 21> Prof. H. y. Wilson (1888) found very pronounced 

 reflections in the early stages of the development of the coral 

 Manicina areolata. These push away the endodertn of the 

 coelenteric surface of the stomod?eum, and Wilson considers 

 them to be there concerned with the formation of the filaments, 

 except those belonging to the first pair of mesenteries. These 

 originated as direct downgrowths along the column-wall, to the 

 mesogloea of which the stomodseum at an early stage is apposed. 



Prof. McMurrich (1891, p. 320, pi. xiii. fig. 17) also describes 

 and figures a reflection at one end of the stomodseum of the larva 

 of Hhodactis Sancti-Tliomce. 



In several cases I obtain an appearance closely resembling 

 that given by McMurrich ; and on following it down, section by 

 section, the deeply-staining tissue is seen to enlarge until ulti- 

 mately it extends all round the oesophagus, with the exception of 

 the two points from which the first pair of mesenteries are given 

 off (fig. 18). At these it passes along the edge of the mesenteries. 



