Sea Lilies. 5 



radials, and immediately upon these rest a third series of five, 

 very like the plates of the other two rows, only their upper 

 surfaces rise into a cross ridge in the centre, and they have 

 the two sides bevelled off like the eaves of a gable, to admit 

 of two joints being seated upon each of them instead of one. 

 This last series of plates are the radial axillaries, and above 

 these we have the first bifurcation of the arms. These three 

 rings of radial plates form the true cup. In the modern 

 species they are very small, but in many fossils they acquire a 

 large size, and enclose, frequently with- the aid of various rows 

 of intermediate or interradial plates, and of a row of basals, a 

 large body-cavity. The two upper plates of each ray are 

 separated from those of the ray next it, by a prolongation 

 downwards of the plated skin which covers the upper surface 

 or disk of the body, and which will be described forthwith. 



Seated upon the bevelled sides of each radial axillary plate 

 there is a series of five joints, the last of the five bevelled again, 

 like the radial axillaries, for the insertion of two joints. 

 These five joints are the first brachials, and from the base of 

 this series the arm becomes free. The first of the brachial 

 joints, that is to say, the joint immediately above the radial 

 axillary, is, as it were, split in two by a peculiar kind of plate 

 joint, called by Miiller a syzigie. All the ordinary joints of the 

 arms are provided with muscles, producing various motions, 

 and binding the joints firmly together. The syzigies are not 

 so provided, so that the arms are easily snapped across where 

 these occur. This is a beautiful provision for the safety of an 

 animal which has such a wide and complicated crown of appen- 

 dages. If one of the arms get entangled, or fall into the 

 mouth or claw of an enemy, by a jerk the star-fish can at once 

 get rid of the embarrassed arm, and as all this group have 

 a wonderful power of reproduction of lost parts, the arm is 

 soon .restored. When the animal is dying, it generally breaks 

 off its arms at these syzigies, so that almost all the specimens 

 which have been brought to Europe, have arrived with the arms 

 separate from the body. About six arm-joints or so above the 

 first, on either branch, there is a second brachial axillary, and 

 a second bifurcation, and on the joint above it another syzigie, 

 and seven or eight joints farther on, another, and so on, but 

 more irregularly the farther from the centre, till each of the 

 five primary rings has divided into from twenty to thirty ulti- 

 mate branches, producing a rich crown of more than a hun- 

 dred arms. Each division, counting from the radial axillary to 

 the tip, is formed of upwards of a hundred joints. The upper 

 surface of the arm-joint is deeply grooved, the lower arched, and 

 from one side of each, alternately, on either side of the arm, 

 there is jointed a series of from about fifteen in the middle of 



