340 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Perrier refers to the ligament masses as true muscle, calling them hyaline 

 muscles in contrast to the brown ventral muscles which he designates as refractive 

 muscles. 



Hamann and Eeichensperger followed Perrier, while Bosshard reverted to the 

 earlier conceptions of J. Miiller and the Carpenters, who considered the ligaments 

 as merely elastic tissue. 



The detailed structure of the ligaments is most readily understood when taken 

 up in connection with their development. As this has only been worked out in 

 regenerating pinnules and arm tips the discussion of this part of the subject will 

 be reserved for the section on regeneration (p. 429). 



There is no connection whatever between the fibrillse of the ligaments and the 

 organic base of the skeleton. 



The rich innervation of the ligament masses, as well as the difference in stain- 

 ing properties, show conclusively that they are not of a connective tissue nature. 

 Eeichensperger believes that this innervation should be interpreted as showing 

 that the ligament masses, especially of the syzygies, which are composed of liga- 

 ments alone, are predetermined foci for autotomy. 



Often, especially when the ventral musculature is fully extended, remarkable 

 wave-like figures appear in longitudinal sections through the dorsal ligament mass 

 which distantly resemble the so-called contraction knots in smooth muscle cells. 

 The staining of the knots approaches that of true muscles, while the intermediate 

 regions take the usual stain of the dorsal ligament. 



There is a slight diiference between the staining properties of the interarticular 

 ligament masses and the fibers in the pit just beneath the center of the transverse 

 ridge in the dorsal ligament fossa, and those of the dorsal ligament bundles and the 

 ligament bundles of the synarthries and syzygies, and in these places the ligament 

 bundles are more closely packed together, but no other difference between the 

 ligaments of these regions can be found. 



Microscopically it is seen that the syzygies usually tear apart across the middle 

 of the fibers and seldom in the region of the loops. Apparently as a result of 

 stimulation of the nerA-es a sudden over-contraction of the fibers occurs, and the.se 

 part more or le,ss in the center. 



Autotomy takes place very quietly, without convulsive movements. Eeichen- 

 sperger doubts that, as has been suggested, autotomy can follow mechanically from 

 a rolling up of the arms. 



Autotomy is frequent at the synarthries between the elements of the IBr 

 series, as well as between the first two brachials. 



At muscular articulations it is in the highest degree exceptional. "When 

 it occurs the dorsal ligament first tears across, and later the ventral muscles are 

 ripped apart. The broken surface presents a confused mass of ligaments and 

 muscles, and regeneration is somewhat less prompt than after fracture at a syzygy 



The ligaments in the Comasteridse and in Isocr'mns are identical with those 

 in Antedon. 



