REPORT ON THE ACTINIARIA. 39 



under the microscope, it consists of a muscular lamella pleated into unbranched folds, 

 which lie closely together like the leaves of a book, are highest in the middle of the 

 tract, and gradually decrease in size on either .side till they pass into the smooth 

 fibrillar layer of the wall. 



The constitution of the oral disk of the specimen examined could not accurately be 

 determined, as it was closely folded in consequence of the extreme contraction. Its 

 peripheral margin bore three alternating rows of tiny tentacles, which only projected 

 like small buttons, and corresponded in number to the individual septa. On transverse 

 section, the tentacles of the inner circle proved to be evaginations of the intraseptal, 

 whilst those of the outer circles belonged to the interseptal spaces. 



The radial muscular fibres of the oral disk (PL VII. fig. 1) are mesodermal, but 

 otherwise only slightly developed. Sparse thin bundles are separated from the ectoderm 

 by a narrow layer of connective substance, and connected like a net with one 

 another by an interchange of fibres. They enter the bases of the tentacles and extend to 

 their points. There were apparently no openings in the tentacles. 



The pedal disk is of no great interest. A small circular ridge, caused by a thickening 

 of the supporting lamella, ran on its inner side between the septa, at a little distance 

 from and parallel to the margin. As I only examined a single specimen of this Actinia, 

 it is impossible to determine whether this structure is constant or not. 



The species before us is chiefly characterised by the size and disposition of the septa, 

 of which I therefore give a more detailed description. It is diificult, on the whole, to 

 recognise in their arrangement the regularity shown by the Hexactiniae. The six 

 pairs of principal septa, of which two lie as directive septa in the sagittal axis, are 

 certainly distinguished at once by their size, but the six pairs of the second order are 

 very small, and in this respect fall short of the twelve pairs of the third order. All the 

 septa already mentioned reach to the oesophagus, whilst those following are imperfect. 

 Of these the twenty-four pairs of septa of the fourth order are always present, but un- 

 equally developed, being larger in the neighbourhood of the principal septa, smaller in 

 the neighbourhood of the septa of the second order. This latter region is, therefore, 

 plainly retarded in growth, and this becomes still more conspicuous in the following 

 septa. In the interseptal spaces, which are contiguous to the septa of the second 

 order, the septa of the fifth order are extremely small, and those of the sixth order 

 are still completely wanting. On the other hand, in the neighbourhood of the principal 

 septa, the septa of the sixth order are already as large as those of the fifth order. It is, 

 however, quite possible that the irregvdarities just described become equalised in the 

 course of growth, as the specimen examined was a young animal without any indication 

 at all of reproductive organs. 



The muscles of the septa show peculiar conditions, especially the longitudinal and 

 parietobasilar muscles. The former is only distinctly present on the septa of the first 



