68 HI U.KTIN 82, INITKD STATES NATIONAL MUSEUM 



food is certainly very plentiful, consisting for the most part of Chlorophyceae, but 

 that ''i'' matter i- inconsiderable >>r wholly absent. 



MORPHOLOGY OF THE COMBS AND THEIR BIOLOGICAL FUNCTION 



GisK'ii noted thai die Comasteridae difTor from all the other comatulids except 

 the Eeliometrinae in the possession of the so-called combs, which usual!}- appear 

 on the proximal pinnules but sometimes are found far out on the distal parts of the 

 arm in Oomaster and in occasional species [or individuals] of Comanthus {Vania), 

 I anthina, and Captilaster. In die Ileliometrinac rudimentary or fairly well 

 developed combs appear on one or more of the proximal pinnules. The genus Coma- 



■ (see Part 3, page 288) is supposed by Gislen to belong to this subfamily of the 

 Antedonidae. It has been observed (see Part 2, page 95, fourth paragraph) that in 

 Heliometra glaeialia the terminal segments of the arms and pinnules are devoid of 

 ambulacra] grooves. Gislen points out that we thus find the remarkable coincidence 

 that in a group not belonging to the Comasteridae, in which the ambulacral furrows 

 are unusually short, combs reappear, and that a change sets in suggesting a reduction 

 of the ambulacral furrows. He recalled that the intestinal contents in Heliometra 

 show remarkable differences from those of the rest of the comatulids catching plank- 

 ton or detritus. 



The combs are developed at the ends of the pinnules. Only occasionally, as in 

 Comantheria or Comanthus, are the most distal segments of the combed pinnules 

 smooth. In Comatonia teeth appear on P, and P, almost from their bases. The 

 teeth are usually developed on one side only, and are ranged in a single row on the 

 side away from the mouth. In Nemanter, Comanthina, and Comanthus two rows of 

 teeth occur, an inner row of large teeth, and an outer row of small ones. 



Transverse sections through the proximal combed pinnules and the distal pin- 

 nules of Comantheria delicata grandis show that, at least in this form, a small interior 

 tooth occurs inside the large exterior tooth, as in Nemaster, etc., although it is not 

 discernible to the naked eye. The sections make it evident that these teeth are derived 

 from the dorsal hooks that occur in most of the comatulids and are especially well 

 developed in the Comasteridae; these have increased in size and have made their way 

 up on one side of the pinnule. Usually on a pinnule that has not been transformed 

 three dorsal hooks stand in a transverse row on the distal segments. When enlarged 

 to form a comb the hook situated most adorally gains the preponderance and surpasses 

 the others, which become more or less suppressed, in size. In regard to its combs 



aster shows its primitive character in the occurrence of two rows of teeth in the 

 comb. The inner row is less evident in the more specialized genus Comaster, although 

 quite distinct in sections. In Comanthus pinguis, in which the comb shows a pre- 

 sumably secondary tendency to reduction, the inner row of teeth is very indistinct. 



In contrast to the distal ends of the other pinnules, those of the combed pinnules 

 may be rolled into a tight spiral, as one of the interpinnular muscles, always the aboral, 

 is very strongly developed. This muscle continues through a large part of the seg- 

 ment, penetrating deeper on the proximal side than on the distal, and so locating the 

 thin dividing wall between the muscles of the articulations somewhat distally of the 

 center of the ossicles. As a consequence of this exceedingly one sided muscular 

 development, the muscular side of the pinnule is much enlarged. The intruding 



