68 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



(2) In the comatulids this process is always invoked to produce a greater 

 number of arms than 10; the young animal always has 10 arms until a con- 

 siderable size is reached, when the arms are broken off either at the first syzygy 

 or at the first synarthry, and from the stump an axillary is regenerated bearing 

 two or more arms in the places of the one lost; this is known as Adolescent 

 autotomy. 



Autotomy at any other place than the first syzygy or the first synarthry 

 always results in the regeneration of a single arm similar to the one lost, though 

 with a longer and more irregular intersyzygial interval (see Regeneration). 



Adolescent autotomy is caused by natural growth changes in the arms, 

 and is not in any waj r subject to the will of the animal (see pp. 140-142). 



Axial cavity. The small hole left in the dorsal pole of the centrodorsal after the 

 loss of the larval stem. It is almost immediately closed by a deposition of 

 calcareous matter (see fig. 594, pi. 16, and pp. 228, 229). 



Axial cord. (1) The large nerve cord which runs along the arm in the canal (the 

 central canal) just anterior to the transverse ridge seen on the joint faces (see 

 figs. 31-34, p. 71, 63, 64, p. 89, and 65, p. 91 and pp. 350-354). 



(2) This term is sometimes used to include all the nerves belonging to 

 the dorsal nervous system. 



Axial interradial canals. The more or less complete canals in the interior of the 

 radial pentagon which lie on the sutures between the radials. 



They inclose branches from the water vascular system (see pp. 375, 376). 



Axial interradial furrow. The furrows seen on the inner side of the radial pentagon 

 which coincide in position with the sutures between the radials; when bridged 

 over by calcareous deposit they form the axial interradial canals (see pp. 375, 376). 



Axial nerve cord. See Axial cord. 



Axial prolongation. A prolongation of the radial canals of the water vascular 

 system whereby they come to end upon the ventral surface of the centrodorsal, 

 or even to extend outward between the centrodorsal and the radial pentagon 

 (see figs. 252-255, p. 253, 256-261, p. 255, 468-470, p. 359, 471-476, p. 361, 

 477, p. 363, and 508, p. 371, and pp. 374, 375). 



Axial radial canals. The ladial canals of the water vascular system, when more 

 or less surrounded by calcareous deposit. 



Axial radial furrows. The furrows on the ulterior surface of the radial pentagon 

 which when bridged by calcareous deposit form the axial radial canals. 



Axial skeleton. The Eadial skeleton. 



Axillary. An ossicle at which the arms divide ; a single ossicle which bears distally 

 two similar series of ossicles arising from a pair of similar muscular articulations 

 (see figs. 1, p. 60, 3, p. 62, 14, p. 65, 30, p. 71, and 61 a-c, p. 87, and pp. 358- 

 360). 



Axis. The axes commonly considered in the description of the comatulids are: 



(1) Anteroposterior axis. This axis divides the animal into two 

 bilaterally similar halves; it is found in two positions, a (1) primary and 

 a (2) secondary. 



