MONOGRAPH OF THE EXISTING CRINOIDS. 



161 



of the protoplasmic plexus forming the organic basis of the skeleton. In the 

 neighborhood of each of the two apposed surfaces the fibrous elements of this 

 plexus assume the character of closely placed parallel connective tissue fibers with 

 no pigment granules nor nuclei embedded in them, but staining deeply with picro- 

 carmine, while the normal protoplasmic basis of the inner part of the calcareous 

 segments is but little affected 

 by this reagent. These fibers 

 pass from the organic basis 

 of one segment into that of 

 the next adjacent so that the 

 two are firmly united, and 

 the superficial denser layer 

 of calcareous tissue is de- 

 posited around their ends. 

 The superficial layer of cal- 

 careous reticulation which oc- 

 cupies the small intervals be- 

 tween the ends of the fibers 

 thus becomes extremely close 

 and compact, but the central 

 portion of the fibrous tissue 

 does not calcify, remaining 

 as a thin layer of fibrous sub- 

 stance between the two ap- 

 posed surfaces. 



Carpenter, like his father, 

 and all students of the re- 

 cent crinoids until very re- 

 cently, believed that the or- 

 ganic or protoplasmic base 

 of the skeleton was continu- 

 ous from one ossicle to an- 

 other, but between them be- 

 came modified into COnneC- fig. 2I6. — Latbrai, tiew or specimen of Lissometha alboflav*. 



tive tissue strands. Keichen- 



sperger was the first to show that the ligaments of the brachial articulations are 

 entirely distinct from the organic ground substance of the plates and are formed 

 exclusively of closely packed bundles of fibrillse the ends of which take the shape 

 of loops within the calcareous substance of the ossicles. From Carpenter's men- 

 tion of loops, apparently identical with the loops described by Reichensperger, it 

 would appear that the union between the radials is probably identical in character 

 with the ligamentous portion of the unions between the brachials. 



The union between the radial circlet and the centrodorsal is of the same 

 nature as that between the individual radials, but it is not quite so close, so that 



