TERMINOLOGY. 21 



TERT^IINOLOGY, 



Or a descriptive analysis of the comjioiici)f elements of the test of the Echinoidea. 



The test of the Echinoidea is composed of tlie following parts : 



a. Five ambulacral areas. 



b. Five inter-ambulacral areas. 



c. Ten poriferous zones. 



d. Vent- opening and anal plates. 



e. Month-opening, peristome, buccal membrane and plates. 

 /. Five jaws when organs of mastication exist. 



(/. Tubercles of various sizes, developed from the outer surface of the plates. 

 //. Spines of different forms and dimensions, jointed with the tubercles. 



These are the essential parts to be known ; others, of secondar}^ importance, will be 

 described in their proper place in the Monograph. 



The hodt/of the Echinoidea is divisible into three parts : — 1st. The calcareous envelope, 

 or skeleton, which has a globular, circular, oval, pentagonal, hemispherical, conoidal, or 

 discoidal form, and is composed of a framework of hexagonal, pentagonal, or polygonal 

 calcareous plates. This testaceous box is called the test; it is the/o/w, the test, of 

 Agassiz ; the (jeneral form, the test, of Desmoulins ; h coquitle, d'Orbigny. 



machine, for they came up adhering by their spine-covered arms to the last fifty fathoms of the sounding- 

 line, not as voluntary exiles from below, but owing to their having coiled themselves around a material 

 from which they found it impossible afterwards to disengage themselves. Now, apart from all other 

 evidence, the facts in connection with this particular sounding were sufficient to indicate that the star- 

 fishes had been raised from the sea-bed itself, and had not grasped the line whilst floating in some stratum 

 of water intermediate between it and the surface. But, by a singular piece of good fortune, the question 

 as to their last resting-place admitted of definite determination on evidence that they bore along with 

 them. To comprehend the value of this, it is necessary to mention that, by means of a separate observa- 

 tion taken upon the same spot, the bottom was found to consist almost entirely of the minute shell-covered 

 organisms (Foraminifera) already referred to ; and faking into consideration the fact that many of the shells 

 were completely filled with the gelatinous substance of which their bodies are composed, and, lastly, the fresh 

 appearance of this substance, the probability is very great that they, in common with the star-fishes, had 

 lived and multiplied at the bottom. But the only circumstance which ought to be accepted as direct proof 

 of their vitality, namely, motion after reaching the surface, was wanting ; as it well might be, since 

 the passage through the vertical mile and a half of water occupied nearly an hour, and the change of 

 conditions to which the creatures became subjected during that period must necessarily have been very 

 great. Nevertheless, the chain of circumstantial evidence was rendered complete ; for, on examining the 

 stomachs of the star-fishes, they were found to contain the minute shelled creatures in abundance, thus 

 clearly establishing the fact of the star-fishes having attached themselves to the sounding-line whilst it 

 rested on the bottom, and adding the strongest confirmation to the view that the minute creatures referred 

 to were brought up from their natural habitation." (Dr. Wallich, " On the Deep-Sea-Bed of the Atlantic, and 

 its Inhabitants;" ' Quarterly Journal of Science,' No. 1, p. 40.) 



