REPORT ON THE ACTINIARIA. 



•JO 



longitudinal furrows. All the swellings of the wall and of the pedal disk are caused 

 by thickenings of the supporting substance. 



The oral disk is smooth and very firm. Moseley has given a perfectly correct account 

 of the manner in which the tentacles are distributed on the oral disk. The principal 

 tentacles are placed on the margin, exactly where the oral disk and the wall meet 

 at right angles. Among these are six tentacles, recognisable on closer observation 

 as the largest, which are disposed at equal distances, two of them, occupying the ends 

 of the sagittal diameter, running through the corners of the mouth. The next six 

 tentacles stand in the middle of the interspaces between the first six, which they nearly 

 equal in size. On the other hand, there is a noticeable difference of size between the last- 

 named six tentacles and the twelve following, and further between these twelve and the 

 twenty-four tentacles composing the last cycle. Whilst, therefore, there are in all forty- 

 eight marginal tentacles, the number of the intermediate tentacles only amounts to 

 twenty-four, which are distributed in three circles. Six tentacles, furthest in and nearest 

 the oral opening, are placed upon the same radii with the six marginal tentacles of the 

 first order ; six others follow a little further out, and twelve others still further out, the 

 former of which correspond to the marginal tentacles of the second, the latter to those of 

 the third order. The first-named six are the largest, but even they are hardly so large as 

 the smallest among the marginal tentacles. 



All the tentacles are knobbed, and therefore consist of a stalk and an expanded vesicular 

 end. The stalk is stiff" and thick-walled, and bears a very thin layer of ectodermal longi- 

 tudinal and endodermal circular muscular fibres. The head is thin-walled, without 

 muscles, and not pierced by a terminal opening. 



The oral opening and the oesophagus are very small. The fissure-like form, usually 

 so distinct, is hardly recognisable, and has therefore been overlooked by Moseley. On 

 closer examination, however, we find even here the two oral angles and oesophageal 

 grooves, which differ very little from the numerous indentations of the oral margin and 

 the longitudinal furrows running out from them. The corners of the mouth and of the 

 oesophagus are more closely defined anatomically by the insertions of the directive septa. 



There are altogether twenty -four pairs of septa : the first six, the principal septa, 

 and the following six, secondary septa, are fastened to the oesophagus, even though the 

 latter do not reach so far down as the former ; the remaining twelve are imperfect. All 

 the septa are plates of equal strength, which is essentially due to the thickness of 

 the supporting lamella. The muscular system is extremely weak and simply arranged, as 

 transverse fibres run on the one side and longitudinal fibres on the other in what is 

 hardly even a slightly pleated layer. Septal stomata are wanting also in the complete 

 septa (fig. 6). 



The ovary, an oval body consisting merely of few broad transverse folds, lies iu the 

 middle of each septum, not excepting the directive septa. The excellent state of 



(ZOOL. CHALL. EXP. — PART XV. — 1882.) P 4 



