146 Proceedings of the Royal frisk Academy. 



Sections of a division of the body above the entevostome -level show the 

 character of the musculature. The fifth-cycle mesenteries hardly project 

 beyond the endoderm, and bear parietal muscles PL XIX. fig. 6), with fairly 

 slender, blunt, well-defined, simple, and branched processes, not more developed 

 on one side than on the other. All tin- other mesenteries have similar parietal 

 muscles, varying a little in size according to cycle, in the larger mesenteries 

 rather better developed "ii the endocoelic than on the exocoelic face. At the 

 level of my sections there is no special development of the transverse muscu- 

 lature—simply a straight line on the exocoelic sides of the mesenteries. The 

 fourth-cycle mesentei eproductive septa, and their longitudinal muscle 



amounts to a f ring dy.not a pennon: their gonads are immense. The third- 

 cycle mi ■ - have diffuse pennons, which die off gradually, in the direc- 

 tion of the body-wall, into a mere fringe of fibres; distally, the pennon dies 

 nil' more or less abruptly in different cases, but always more rapidly than it 

 does proximally. Tin- pi rming it are stout and very well branched, 



but not Btout enough to give tin- " • ippearance I PI. XIX. fig. 9 1. 



The perfect mesenteries, as exemplified by the pair Bectionized, have fair 

 pennons of peculiar form, whose highest point lies about the middle of the 

 mesentery 'PL XVIII. figs. 5 and 7 . The pennon forms a bulge, as it is 

 supported on a large branching lobe or hill of mesogloea; it is not exactly 

 M diffuse," but not far from it. essentially. Its processes vary in different 



a to be stout enough to give the " reversed " 

 aspect, sometimes they are hardly bo. But they are not of the slender, 

 feathery, or twig-like type. 



(ii» Sphi irter.— Strong and well developed. Not specially long, but broad 

 above PL XIX, fig •"■ . Below it tapi gularly and fairly rapidly to a 



point. I I from the endoderm throughout by a wide band of clear 



in-- :;d has a fairly clearly defined inner edge. Throughout its upper 



part it fills most of the thick mesogloea, and at its outer edge it thins away, 

 and comes ratliei the ectoderm. The structure is very characteristic — 



. the alveoli frequently Ij s aether closely in groups, as it were 

 ver c mb-divided (PL XVI II, fig. 21 . These groups and the single 



■li are well I from one another by mesogloea: they are most 



densely packed in the uppei part, and least bo in the middle. There is a 

 tendency towards vertical layering chiefly above and also to arrangement in 

 horizontal li: ially in the middle part . In some sections the alveoli 



at the very top lie ■ . tle-r that they form a reticular patch. 



— 1 ture of the oral disc is more interesting 



than any I i PL XIX. fig. 4 . It has very high ridges of two sorts, 



ilarly alternating ; the smaller and simple) one- biidgc the exocoels, the 



