14 SVEN LOVEN. EcniINOLORICA. 



the interradimn, in sucli a iiiaiiner tliat, for instance, of the 

 two retra<!tors of the pyramid 5 one comes from the plate I a, 

 the other from the V h. Consequeiitly each ambulacrnm sup- 

 plies one retractor to each of two different but contiguons 

 pyramids. They are inserted upon the sides of the pyramid 

 on its under, narrowed part. The two protractors, m. pro., 

 are, in this aspect, seen under tlie retractors, coming into 

 view close together from under the margin of the solitary in- 

 terradial plate, and descend, diverging, towards the sides of 

 the upper, broader part of the pyramid. All tliis is seen 

 again, under the opposite aspect, when tlie preparation is tui'- 

 ned över, fig. 26. The ocsophagus is seen in the centre witli 

 tlie folds by whicli it is suspended. The rotula; are well de- 

 veloped. as are also the compasses, the epiphyses, and all the 

 external muscles, the m. radiales Stewahd, the protractors, 

 m. pro., and the retractors m. re. The former, m. pro., arise 

 close together on the peristomal margin of the solitary inter- 

 radial. and ascend, diverging, towards the epiphyses on which 

 and on the vipper margins of the pyramids they are inserted. 

 The retractors, m. re, of each pyramid arise far apart, each 

 from a point near the outer margin of a different ambulacral 

 plate. At this jjoint of attachment the auricular branch is 

 commencing to form, a low projection of calcified reticular 

 tissue; its basis extends a little beyond the near suture, upon 

 the solitary interradial that separates the two auricles. From 

 these widely distant points of attachment the retractors de- 

 scend slightly convergiug, as it was seen in the oral aspect, 

 fici. 25. 



The calycinal system, fuf. 27, occupies a very considerable 

 part of the dorsal aspect. It has still much of its normal 

 condition and is less modified than that which 1 formerly de- 

 scribed. ' The dorso-central disk is entire and well-developed. 

 Opposite the costals 2, ;>, 4 it still retains the rectilinear sides 

 of its normal pentagonal ligure, and the lozenges of parallel 

 internal rods that cross the straight sntures, are intact. It 

 is otherwise on its line of contact with the costals 1 and 5. 

 There the transformation has alreadv commenced, which is to 

 result in the total conversion of the compact dorso-central 

 piece into the flexible anal membrane.- The lozenges have 



' Etudes s. 1. Echinoulée.s. p. G9, Pl. XXI. fig. 171. 

 ^ Ib. fig. 171—176. 



