138 Proceedings of the Royal Irish Academy. 



on the side of the mesentery which does not hear the pennon. They soon 

 die out, and on the retractor-side of the mesentery are followed by a wavy 

 fringe of fibres, gradually rising into processes, which finally form a fairly 

 strong pennon (PL XVIII. figs. 9 and 12 ). Typically ihis ends rather abruptly, 

 distally, and is succeeded by another fringe of insignificant processes. 



The pennon processes are fairly high and branched, so stout that they are 



very el - a _ the " reversed " appearance very markedly. It 



will lie noted from the figure that they look just as if they were projecting 



a '-a — which is left white and not shaded. The second and 



third cycle mesenteries have a fringe of longitudinal muscle processes which 



has hardly the distinction of a pennon ; and they have larger parietal muscles 



than the primaries. Those of the fourth cycle have practically nothing but a 



and those of the •• have parietal muscles only. 



— M . not long or large. Its outline is irre- 



gula odermal and endodermal surface-fissures caused 



by wrinkles. It tted throughout from the endoderm, but comes very 



.'rm in some li tapers off into a "tail" below, and 



ends as _ st in central parts. In structure it 



is not definitely " alveolar " ; but the I a •■! in clusters am] in 



distorted crushed, and Battened cavities, and I onn with each other 



ger clumpe tend to l> _ I in transverse and longitudinal lines, 



and 



liiii . — The radial musculature of the disc is partly 



lermal, parti Ided in I adoea.il has a rather peculiar 



chai PI. XVII : b 7 The muscle-layer is very thick and 



- . 1 in those radii of the disc which bridge the space between 



17 ; but in the radii between the two mesen- 



er reaches the mesentery, it thins 



out gradually, so that, when tl irked, it has thinned away almost 



to i. the middle of the radius. The thinning is more marked 



iir than between two of a small pair. 



In ' i t and y is one partner 



- thick parts the layer is to a considerable extent 



d in the a ea, the fibres forming clumps and even little rings 



The thicknesses of the three 1 the tentacles varies according 



ut of course the mesogloea is excessively develop 



in the basal swelling*, which have a thin but ireguhu \ial coating. The 



longitudinal musculature is ectodermal PI Will. fig. 11 . borne on short, 



stout, practically anbrancl low but continuous round the 



_ 



