VON BUCH ON THE CYSTIDEA. 25 



Plications, Strice and Pores of the Plates, — These markings are 

 not only in the highest degree instructive in the whole family of 

 Crinoidea, but a close investigation teaches us also, that there exists 

 with regard to them a law of arrangement and a regularity which 

 one could hardly have anticipated in characters apparently so super- 

 ficial. In the first place, the striae of growth, distinctly parallel to 

 the bodies of each plate, repeat the form of the plate quite up to a 

 central nucleus, and hence clearly distinguish each plate from those 

 which are adjacent. These striae, so distinctly marked and projecting 

 so strongly, show the way in which each plate was surrounded on 

 all sides by an organized membrane from which the calcareous mat- 

 ter was periodically deposited, thus enlarging the whole body of the 

 animal by increments applied at each edge of every plate. 



From the centre of each plate there proceed rows of pores, pro- 

 bably the remains of ambulacra, to all the angular points of the po- 

 lygon, each row generally consisting of six pores. Towards those 

 angular points on the side of the polygon the row of pores is single, 

 while in those two directed vertically upwards and downwards the 

 row is double. It is worthy of notice, that with regard to the side 

 plates, only the upper half is decorated with these rows of pores, 

 the lower part having them sparingly or not all distributed ; but 

 on the scapular plates a contrary arrangement takes place, the rows 

 of pores being there most regularly developed on the lower half, and 

 uniting with those from the side plates to form a complete encircling 

 festoon on the upper part of the cup. This is also a very striking 

 peculiarity in Hemicosmites, but such similarity is produced by the 

 uniform action of a general law, and does not prove any identity of 

 specific character. When the rows of pores of the scapular plates 

 are examined minutely with the aid of a powerful magnifier, a very 

 remarkable structure is observed, characterizing them and almost 

 peculiar to them, the isolated pores not being hollow, but covered 

 with very minute vesicles, one in the middle and six smaller ones 

 around it. These little vesicles are larger and more abundant the 

 nearer we approach the middle of the plate, and quite in the middle 

 there are about a score of them close together, so minute as only to 

 be visible under the microscope. 



Not a trace of these vesicles can be discovered on the rows of 

 pores on the lateral plates, and thus the scapular plates may be dis- 

 tinguished very easily from the others, even when only the smallest 

 fragments remain ; and by taking advantage of this structure we 

 may readily discover those monstrosities in which the scapular plates 

 entirely conceal some of the lateral plates and rest immediately on 

 the pelvis, producing indeed a remarkable distortion and compres- 

 sion of the general form, but only on that side on which the mouth 

 is placed. This compression probably has some reference to the 

 effort made by the animal to bring the mouth near the ground in 

 order to obtain food. The pores i)cnetrate the entire thickness of 

 the plates, and arc as distinctly marked on the under as on the 

 upper surface. There was doubtless some organ projected through 

 them from the animal. 



