ASTEROIDEA OF NORTH PACIFIC AND ADJACENT WATERS- -FISHER 157 



ved) small disconnected plates would appear to be of little practical valuo; whereas 

 in age, if calcium metabolism is faulty, stored supplies might woll be more roadily 

 available than that obtained in food. 



In contrast, the marginal, adambulacral, and ambulacral systems are strong 

 and very flexibly articulated. The alternation of ambulacrals mentioned by Verrill 

 (1914, p. 201) is probably duo to faulty preservation since I found no indication of 

 it in large well preserved specimens. 



The ambulacral ossicles distad to the adoral carina rapidly becomo very 01 

 pressed. In a large dry specimen having R 275 to 300 mm. there are about 330 

 ambulacral ossicles on either side, or 660 to the ray. Although there are two lon- 

 giscries of ambulacral pores on either side, the plates are so compressed that the lWrge 

 tube-feet are crowded into six longiseries. When the furrow is fully open it is wide 

 and shallow. In living specimens the great number and sizo of the tube-feet form 

 an impressive spectacle. 



The actinostome is largo and the membranous peristome broad, as the animal 

 is capable of swallowing goodsized sea urchins and molluscs. A section of the peri- 

 stomial ring is shown in Plate 79, Figure 4. The first ambulacral ossicles arc rela- 

 tively smaller than in the Coscinasteriinae. 



The intcrbrachial septum is membranous, extensive, and fortified by irregular, 

 oblique dorsoventral columns of plates and irregular scattered plates of various 

 small sizes. These are apparently better developed in small than in large specimens, 

 in some of which there are very few septal plates present. 



Young. — The majority of young begin life with six symmetrical rays, as deter- 

 mined by Iiitter and Crocker (1900) who examined many specimens from Yakutat 

 Bay, Alaska. "The reef near the anchorage off the Indian village of Yakutat, a 

 large area of which is exposed at extreme low tide, was everywhere strewn with 1 i 

 specimens, and on the Laminaria, which grows here in great luxuriance, were thous- 

 ands of young of all sizes, from a few millimeters in diameter to practically the full- 

 grown state." The smallest of these had only six or eight rays. The number six, 

 however, is not invariable, since a specimen from Bayne Sound, British Columbia, 

 having a maximum R 13 mm. started with five rays. (Text fig. 2.) 



Ritter and Crocker find that new rays arc budded off symmetrically in pairs 

 with referenco to a constant ray A. This ray is between rays I and II, according 

 to the usual system, which starts with the arm adjacent to the madreporite and 

 enumerates the five clockwise. This ray A occupies the position of the larval organ 

 in Asterina gibbosa and Asterias vulgaris and determines a plane of symmetry Which 

 includes more or less perfectly the intestinal coeca, apical radial muscle bands, and 

 the racemose glands. 02 The plane passes through rays A IV. 



It is evident, however, that there must be exceptions to this rule, otherwise the 

 number of rays would always be even, which is not the case. 



It is a curious fact that Ritter and Crocker encountered great uniformity among 

 their many specimens, while of the three very small examples available to me {of 

 study, two exhibit marked exceptions to their rule. These three are from Bayne 

 Sound, British Columbia and are shown diagrammatieally in text Figures 1 to 3. 



•i Proc. Wash. Acad. Sci.. vol. 2, 1900, pi. 13, Bgs 6 and?. 



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