342 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The structure of the ligaments in the columnal syzygies in Isocrinus is identical 

 with that of the brachial syzygies, though here the ligaments are shortened to a 

 minimum and the various elements are more difficult to demonstrate. 



In the column of Isocrinus the pear shaped ganglion cells occur in only limited 

 numbers, except at the syzygies. The ligaments of the internodes mostly run 

 through several columnals and are very deeply embedded in the calcareous sub- 

 stance. Between the syzygies the column is very tough, and broken surfaces always 

 show fragments of the adjacent ossicles. Only at the syzygies does a smooth break 

 occur. 



Keichensperger comes to the conclusion that the fiber bundles of the dorsal and 

 interarticular ligaments in the muscular articulations, and of the syzygies and 

 synarthries, possess primitive muscular attributes and are to be interpreted rather 

 as a primitive type of muscle than as pure connective tissue. But, as he says, 

 additional investigation, especially along physiological lines, is needed to settle 

 the question. 



LIGAMENTS IV THE CIRRI. 



The movements of the cirri have been mentioned by many observers, and 

 it is clear that the ligaments uniting their segments must be capable of independent 

 movement; but they agree in every respect with those in the dorsal and inter- 

 articular ligament bundles of the muscular articulations, and with those in the 

 syzygies and synarthries. 



WATER-VASCULAK SYSTEM. 



The water-vascular system consists of a ring canal about the mouth, running 

 beneath the ambulacral depression, and vessels radiating from this which run 

 out under each ambulacral groove, following its course onto the arms and pinnules. 



Attached to the ring canal is a row of little tubes which open into the body 

 cavity, and which collectively are the equivalent of the so-called stone canal of 

 the other echinoderms. 



A madreporite comparable to that of the starfishes was described in Antedon 

 mediterranea by Delle Chiaje, but it turned out to be a convex parasitic worm of 

 the genus Myzostomiim. Communication between the body cavity and the exterior 

 is maintained by a variable number of pore canals, or calyx pores. Carpenter 

 notes that the early pentacrinoid larva has but one of these, situated in the same 

 interradius as the fore gut; in the later stages of pentacrinoid life and in the 

 young Antedon just free from the larval column there are five, one in each inter- 

 radius; while in the adult Antedon hifida there are about 30 in each interradius. 

 and in HeUometra (jlacialis the number becomes still larger. Ludwig estimates 

 that there are 1,500 in the ordinary adult Antedon mediterranea. 



The calyx pores occur on the oral surface of the disk and on the lateral 

 surface of the arms as far as the second brachial. Except in the immediate 

 neighborhood of the mouth they are less abundant in the anal interradius than 

 elsewhere, and though they sometimes occur on the sides of the disk they never 

 extend far down toward the dorsal side. When the disk is plated the pores may 



