48 THE VOYAGE OF H.M.S. CHALLENGER, 



also towards the oral disk and pedal disk, are weak in the lower parts, but very strong at 

 the upper end. The upper portion draws the oral disk very energetically towards the 

 wall, and is assisted in this by part of the longitudinal fibres. The interspace between 

 the oral disk and wall is here reduced to a minimum, which renders the separation of 

 detached single septa more difficult. The parietobasilar muscle is moderately strong in 

 most septa, and does not even extend up to the third of the height of the animal ; it is 

 not merely connected with the septum by epithelial adhesion, but by coalescence, as the 

 supporting lamellae of both parts are fused to a great extent. The epithelial lamellae and 

 the muscular fibres of the surfaces of the parietobasilar fold and the septum which are 

 turned towards one another still remain, however, here and there between the fused 

 streaks of the supporting lamellae, and in transverse section originate circular figures 

 which are enclosed in the connective substance, and indicate by their serial arrangement 

 the boundary between the septum and the fold. 



Two kinds of stomata are found in the muscular part of the septa ; the peristomial 

 are very large, whilst the marginal, which lie close to the wall, are smaU, and, in fact, so 

 small in the oldest septa that they are almost entirely obliterated. 



The thin-membraned veil-like part of the septum is only furnished with a weak layer 

 of muscles, and bears both the mesenteric filament, which is fastened to its free margin, 

 and the reproductive elements, which in Dysactis are not rolled up into compact masses 

 as they are in most Actiniae. The follicles of the testes in the male, the ova in the 

 female are scattered over the supporting lamella, which, consequently, has the look of 

 being strewed with isolated star-Hke points. The filamental apparatus appeared to be 

 present in the ova. 



A remarkable diversity usually prevails in the development of the septa. The 

 directive septa are very small, but, on the other hand, they are connected to a great 

 extent with the oesophagus, as the latter, in correspondence with them, is produced 

 into the long oesophageal lappets, which reach nearly to the pedal disk. The thin- 

 membraned part is small ; all the muscles, especially the parietobasilar muscle, stronger 

 than on any other septa ; reproductive organs wanting throughout. The directive septa 

 agree in the last respect with the other principal septa, and also with the six pairs of 

 septa of the second order, which are chiefiy distinguishable from the principal septa by 

 not extending so far on the oesophagus. We first find the reproductive elements richly 

 developed on the twelve pairs of septa of the third order ; they are present on all other 

 septa, with the exception of the unimportant rudiments of those of the sixth order ; on 

 the other hand, the muscular parts of the septa become almost imperceptible, and they 

 themselves no longer project so distinctly into the gastric space. Only the septa of 

 the third and fourth orders still reach the oesophagus, though their insertion occupies no 

 great space ; the septa of the fifth order end on the oral disk. 



It is remarkable that from the third cycle of septa onwards, the septa of one and the 



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