REPORT ON THE ACTINIARTA. H3 



that the epithelium of the hoily-surfa.ee sinks like a funnel into the mesoderm, where it 

 is prolonged into a broad or narrow canal which soon begins to throw out branches 

 (%. 2). ' 



The ectodermal epithelium is covered by a fibrous cuticle, which recalls the 

 " epidermis " of Phellia pectinata and Cereus spinosus. The endodermal epithelium has 

 produced a thin, circular muscular layer, and is traversed by small, roundish, sharply- 

 contoured bodies. I consider these bodies as parasitic, unicellular organisms of the 

 same kind as those which my brother and I have already observed in various species 

 of Actiniae. There was no visible trace of the usual yellowish and greenish colour, 

 but this was probably owing to the preservation in spirit. 



In the inverted part of the wall I found a sphincter of a very peculiar nature (PI. 

 XIV. fig. 1). It consists of two perfectly separate portions, a larger, which begins at 

 the outer part of the wall, bends round at the inverted edge, and extends a little way 

 into the invaginated part, and a smaller, which lies at the boundary between the 

 wall and the oral disk. When the animal is expanded, this second portion of the sphincter 

 will lie above the larger portion of the muscle ; when the animal is contracted it occupies 

 the lowest part of the invaginated wall. A space without muscles, which does not 

 contract, and, therefore, becomes pleated, lies between the two portions. 



Both parts of the sphincter are mesodermal and placed at an equal distance from the 

 endoderm and the ectoderm ; their bundles of fibrillse are arranged irregularly and 

 repeatedly crossed and interwoven in their course, so that the same transverse section 

 passes obliquely through some, transversely through others. The bulk of them lies in 

 the inverted part of the wall, whilst the muscles merely form a thin layer in the outer 

 part of the wall. 



The oral disk bears a double corona of small tentacles, corresponding in number to 

 the septa, in that part of its periphery which is contiguous to the wall. The inner 

 tentacles communicate with the intraseptal spaces, the outer tentacles with the interseptal 

 spaces, the two are therefore placed alternately. The muscular system of the oral disk 

 and of the tentacles is ectodermal and extended in a smooth layer. 



The distribution of the muscles can be very well recognised in the septa of the 

 strongly contracted polyps. The longitudinal muscular lamella is pleated both in the 

 small rudimentary septa and in the large septa so as to form a small muscular pennon, 

 whilst the fibrillse which rise obliquely are less strongly developed (PI. XIV. fig. 2). The 

 paired grouping of the septa is consequently very distinct, and we can also easily 

 distinguish the two pairs of directive septa from the ordinary pairs. The number of 

 the latter varies according to the size of the animal. In the largest polyp examined, 

 there were in all twenty-nine pairs of septa (PI. XIV. fig. 3). Of the two pairs of 

 opposite directive septa, one pair is rudimentary, does not bear mesenteric filaments, and 

 does not reach the oesophagus, whilst the other pair is perfect, bears mesenteric filaments, 



(ZOOL. CHALL. EXP. — fART XV. — 1882.) P 15 



