224 Dr. W. B. Carpenter on the Structure [Jan. 20, 



small pieces of the soft parts from the arms of the living adult, I have 

 found currents to be produced in the water surrounding them, which 

 could only be accounted for by ciliary action. Thus the brachial appa- 

 ratus may be regarded, in the first place, as an extended food-trap. 



It may be here added that my examination of various types of existing 

 Pentacrini enables me- to affirm that they are nourished in exactly the 

 same manner, their brachial and digestive apparatus being constructed 

 upon precisely the same plan as that of Antedon, and the contents of the 

 alimentary canal being of the like nature. And this renders it probable 

 that not only the Pentacrini of the Mesozoic period, but the entire series 

 of Glenoids extending through the whole range of geological time, from 

 the " primordial zone " of Barrande to the present epoch, obtained their 

 food after the like fashion. 



In the thickened disk which surrounds the mouth, formed at the 

 junction of the perisome of the oral disk with the wall of the alimentary 

 canal, I have detected a series of csecal tubuli opening into the com- 

 mencement or oesophageal portion of the alimentary canal; these may 

 have a salivary function. And the peculiar gland-like character of the 

 plicated portion of the wall of the inner side of the horizontal coil of the 

 alimentary canal seems to render it probable that it performs the function 

 of a liver. 



Circulating and Respiratory Apparatus. — It has been shown that the 

 true "tentacular" canals constitute a system entirely distinct in the 

 adult from the general canal-system of the arms, although derived like 

 it, in the first instance, from the perivisceral cavity, and that there is 

 no proper oral ring which can be regarded as the centre of the radi- 

 ating tentacular canal. As it has also been shown that the so-called 

 " tentacles " have no share whatever in the ingestion of food, the question 

 arises, what is their function in the economy of the animal? I am dis- 

 posed to think that they are homologous with the tentacular fringe 

 surrounding the mouth of the Holothurida, and with the " respiratory 

 tubes " of the Asterida and Echinida, and that they constitute a special 

 respiratory apparatus, serving for the aeration of a fluid that may be 

 regarded, like the red blood of a Terebella, as not so much nutritive as 

 respiratory*. It is no objection to this view that the tentacles of 

 Antedon are not ciliated on their surface ; for this is true also of the 

 branchial tufts of Terebella and other Annelids having a double respi- 

 ratory apparatus, one for the red blood, and the other for the " chyl- 

 aqueous" fluid. Certain it is that Antedon is more dependent than 

 Echinoderms generally upon the perfect aeration of its fluid, as it soon 

 dies in water that is not kept in a state of tolerable purity, though 

 Ophiurce and OpTiiocomm may thrive in it. 



* It is stated by M. Edmund Perrier that distinct muscular fibres are traceable in 

 the walls of the tentacles ; and these may produce a sort of vermicular contraction by 

 which the fluid of this canal-system is kept in movement. 



