246 J. Rofe — JSfotes on the Crinoidea. 



scales close over them, forming a vault, so that the five channels are 

 converted into covered ducts converging into a common subcentral 

 aperture, concealed beneath the integument and not visible from the 

 outside. In the covered parts of the channels I found masses, con- 

 sisting of microscopic Crustacea, larval bivalves, and other remains 

 of the food of the animal, apparently taken through the ends and 

 open parts of the channels, and on its way through their covered 

 parts to the concealed mouth." The description here given of the 

 ventral disk and the covered channels, to the central internal mouth 

 of the Hyponome, closely agrees with that of similar covered 

 channels on the disk of a Cyathocrinus in my paper above alluded 

 to, and strengthens the suggestion therein made that the mouth of 

 these Crinoids was central and internal, and adds to the probability 

 that the Crinoids as a rule had an in-current, excited by cilia or by 

 the fimbriated pinnulse on the sides of their channelled arms, which 

 passed through the covered passages to the internal mouth. If this 

 is allowed, and in the case of the Hyponome it can scarcely be 

 doubted, there can be little hesitation in assuming that the pro- 

 boscis in some Crinoids and the lateral or interbrachial openings 

 in others, is the anal aperture for the ex-current. In this case 

 the animal being provided with an in-current and an ex-current open- 

 ing, as in the Tunicata, would thus approach the Molluscoidea. 

 In some other respects there appears to be an approximation of 

 some of the Crinoidea to some of the Tunicata, as in the pyramidal 

 valvules of Cystidea and the Chelyosoma; and the outer tough 

 bags of some of the Tunicata also contain radiated concretions 

 sometimes siliceous, but more frequently calcareous, thus approach- 

 ing the test- of the Echinodermata. If also, as is above supposed, 

 the Crinoids received their nourishment and the water necessary 

 for respiration through the arms and the covered channels connected 

 with them by an internal mouth, probably the power of expansion 

 and contraction above alluded to may have been used by the Crinoids 

 for the purpose of rapidly ejecting water to clear the internal 

 passages, as is done by the Ascidium or sea-squirt, and by the mol- 

 lusca generally. 



No doubt many objections maybe raised to this supposed approach 

 of two different and perhaps distinct orders; we know, however, 

 that nature draws no hard lines, but abounds in connecting links, 

 and it may be possible that the Molluscoidea and the Echinodermata 

 are connected by the link now suggested. 



EXPLANATION OF PLATE VI. 



Fig. 1. Plate of the column of recent Pentacrinus caput-medusce, after boiling in 



Liquor potassa. Magnified seven times. 

 a. a. a. The five radiating elliptical lobes. 

 Fig. 2. Cross-section of another plate, similarly treated, showing the tubuli and 



pores. 

 Fig. 3. Plate of column of same, decalcified by very dilute Muriatic acid, and then 



allowed to dry, showing the central axis and the shrunk lobes. 

 Fig. 4. Joint from one of the side-arms in the column, boiled in Liquor potassa. 

 Fig. 5. Unprepared side-arm, broken oflf, showing the fibres projecting from the pores. 



