14 THE VOYAGE OF H.M.S. CHALLENGER. 



sliglitly arborescent, as is shown in PI. II. fig. 2, and arranged close to one another 

 like the leaves of a book. At the free edge of the pleat the musculature is 

 interrupted, since here the fibres of the mesogloea, which serve as foundation for 

 the muscle-pleat, radiate into the epithelium. For some distance they are united 

 in a bundle ; they then part, and each fibre individually tends in the direction of the 

 epithelial surface. The ner\'e-fibre layer is consequently pierced by fine fibrils, arranged 

 parallel to and at equal distances from one another. I would have gladly determined 

 how far the connective tissue fibres reach, and whether they are connected with indi- 

 vidual epithelial cells or not ; but in thin sections I could only follow them into the 

 dim granular striated layer of epithelial cells, in which they were no longer distin- 

 o-uishable from other fibres. Attempts to exhibit the isolated fibres by brushing and 

 ao-itatino- thin sections, or by maceration in alkali, yielded no result ; and staining with 

 picrocarmine was also unsuccessful. The latter generally stains the mesogloeal struc- 

 tures of a deep red, and is therefore peculiarly adapted for exhibiting the mesogloeal 

 lamina which carries the muscles, but it refuses to differentiate the fibrils. The red 

 tint is therefore onlj^ seen to extend so far as is expressed in the figure b)'' shading ; 

 the fibrils probably do not stain, but only the cement substance uniting them. The 

 condition here described may be followed on to the oral disc, inasmuch as the sup- 

 porting laminae of the muscle pleats here also run out in fibres, and the individual 

 fibres radiate to the epithelium. I have only further to remark that radial furrows, 

 shallow and slightly expressed, run from the edge of the oral opening towards the 

 tentacles. 



The stomatodseum, in the only specimen which I could examine, was evaginated, 

 and consequently so tightly stretched that even the siphonoglyphes were almost 

 smoothed out, and hardly recognisable. 



The mesenteries agree in number with the tentacles ; all reach the stomatodseum, 

 and bear generative organs. The younger mesenteries touch tlie stomatodseum some- 

 what further back, and are in other respects less developed than the older ; but their 

 generative organs are more voluminous than those of the first and second orders. 

 Stomata in the mesenteries, and acontia, I have not been able to recognise. 



Family 3, Actinid^, A. Andres. 

 AntJieadai, Hertwig. 



Genus Hormathia, Gosse. 



Actiniae with broad difi"use endodermal sphincter; smooth thin body-wall, and 

 parietal spherules {i.e. marginal spherules placed on the body-wall). • 



