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



tlirougliout ; their longitudinal muscular fibres are developed into a repeatedly 

 folded muscular lamella, whilst their transverse fibres are weak. The parietobasilar 

 muscle, which springs from the small pedal disk, and reaches half-way up the wall, is also 

 weak (fig. 2). 



The greater part of the thin-membraned portions of the septa had been torn away ; 

 where they still remained they lay in the interseptal and intraseptal chambers, from 

 which they protruded through the stomidia. They contained the reproductive organs, the 

 specimen examined by me being a male. The follicles, filled with spermatoblasts and 

 spermatozoa, are not so thickly compacted as in most other Actiniae, but rather isolated and 

 of considerable size, so that they can be separately recognised with the naked eye placed 

 beside one another hke paving-stones. 



All the septa reach the oesophagus ; the upper part only of the forty-eight septa of 

 the third order is connected with the oesophagus, whilst the others extend much farther 

 downwards ; they are all pierced by peristomial openings, forming a circular canal in the 

 aggregate. The only diff'erence between the septa — apart from size — seems to be that the 

 principal septa are without reproductive organs. I must, however, remark that in conse- 

 quence of the numerous injuries, it is impossible to make any positive statements as to 

 the distribution of the reproductive elements upon the septa. 



All the surfaces of the wall and of the septa covered with endoderm are browTiish- 

 violet, as numerous pigment granules are deposited in the epithelium. The mesenteric 

 filaments, which I have figured in transverse section in fig. 5, form the only exception ; 

 they are whitish like the ectodermal parts, and are distinguished in this way from the 

 dark ground of the septa on which they run in numerous meandrous curves. 



Family, SAGARTiDiE, Gosse. 



Sagartinoe= Phellinw, Verrill. 



Hexactinise with acontia, a strong mesodermal circular muscle and numerous very 

 contractile tentacles ; the principal septa, or septa of the first order, only are perfect and at 

 the same time sterile ; all the remaining septa are imperfect. 



In my researches on the Actiniae, which have already extended over a very large 

 amount of material, I have almost always found two characters combined, (l) The pre- 

 sence of filaments known as acontia near the lower end of the mesenteric filaments ; they 

 float freely in the gastric cavity, are thickly covered with nematocysts, and if dancrer 

 threatens can be protruded quickly as weapons of defence. (2) The six pairs of principal 

 septa only reach the oesophagus, all the others being imperfect. Eeproductive organs 

 are found only on the secondary septa, of which, however, the older are often per- 

 manently sterile. 



My brother and I first observed these facts in Adamsia diaphana, Metridium dianthus. 



