226 



HYATT, 



the walls in the coenoecium of Cristatella (Fig. 7, E"'),but 

 it does not probably extend into their reticulated portion 

 (PL 14, fig. 1, Q). Judging from the thinness of the lat- 

 ter, and, from the fact, that all the longitudinal muscles of 

 the body appear to be connected more or less with the 

 fourth or epithelial membrane, it is quite likely that the 

 reticulated portion, or those parts of the coenoecial walls 

 which lie between the junctions of the walls with the up- 

 per and lower internal surfaces of the coenoecial endocyst, 

 are composed wholly of longitudinal fibres, encased by the 

 epithelium. Around the invaginated fold of Plumatella 

 the fibres are thickly disposed and form the so called sphinc- 

 ter muscle. This is not a narrow band, as described by 

 Prof. Allman, encircling the lower edge of the fold, but a 

 local development of the transverse fibres, as broad as 

 the fold itself (Fig. 8, E'"). 



In the evaginable 

 endocyst this layer 

 can be seen, by 

 careful focussing, 

 through the fourth 

 membrane, but only 

 with ease, when 

 more or less contrac- 

 ted. 



FIG. 8, Magnified view of the Invaginated fold In the arms and 



of a living specimen of PLUM ATELL A DIFFUSA.* Innhnnhnrp it i* 



A, ccenrecial orifice: D,ectocyst: E', first mem- lopnopn 



brane of the endocyst : E", second membrane of thick, and frequent- 



the endocyst: E'", third layer of transverse mus- i ,i / v 



cular fibre, constituting the Sphincter muscle. ly, in the lormer, DC- 

 E"", fourth or epithelial layer, accompanied by rt^mr/VU-i+o^ 



longitudinal muscular fibres. COmCS Convoluted 



by the action of muscular bands apparently developed in 

 its substance. I was unable to trace this membrane in 

 the tentaclqs, but judging from the great thickness of the 

 second tentacular membrane, and the slight increase which 

 takes place in the transverse diameter of those organs when 



*NOTE. Only three membranes are delineated in the coenoecial endo- 

 cyst of figure 8. This is owing to my want of success in defining the 

 parts of the innermost layer, in the specimen figured, which is undoubt- 

 edly made up of two layers, as in the coencecium of Cristatella (Fig. 7, 



