MONOGRAPH OF THE EXISTING CRINOIDS. 503 



Thomson says that the free-swimming larvae are from 1.5 mm. to 2 mm. in 

 length. The larvae found by Busch in the Orkneys were somewhat smaller than 

 those of Antedon adriatica. 



Thomson notes that the cilia do not vibrate with the regular rhythmical 

 lashing of ordinary cilia, but seem to move more independently, their motion 

 regulating the rapidity and direction of the movements of the animal in the water. 

 The anterior tuft of long cilia is in perpetual vibratile motion. 



The larva swims with either extremity in advance indifferently. It swims 

 rapidly with a peculiar swinging semirotary motion. 



When resting the ventral surface is downward. 



The spicules forming the rudiments of the calcareous plates are at first blunt, 

 irregular cylinders, but shortly they fork at either end and, finally, by repeatedly 

 dichotomizing and anastomosing, they form delicate plates of calcareous network. 



W. B. Carpenter observed that the nature of the objects to which the larvae 

 attach themselves varies with the locality. In Lamlash Bay, Arran, he never 

 found them on anything but the fronds of Laminaria, to which the adults 

 habitually cling, or on bryozoans or Spirorbis growing on these. But at Ilfracombe, 

 where Laminaria is much less abundant, but where on the contrary Salicomaria 

 grows in great luxuriance in the habitat of Antedon, the pentacrinoid larvae 

 are found living on it. In the Bay of Cork Mr. J. V. Thompson found the 

 larvae attached to the various species of Sertularia and Flustracea which occur in 

 the deeper parts of the Cove, in from eight to ten fathoms. Mr. Wiliam Thompson 

 (of Belfast) found them attached to Delesseria sanguined. Usually the larvae 

 are widely distributed over the surface of the object to which they are attached, 

 but sometimes a group of several, showing different stages in development, may 

 be met with. Doctor Carpenter had one specimen showing more than 70 penta- 

 crinoids, all nearly in the same stage of development, attached to the surface of a 

 patch of M embranipora which was encrusting a frond of Laminaria; and another, 

 given him by Sir Wyville Thomson, in which 35 pentacrinoids in the "prebrachial 

 stage" are so closely crowded that the discoidal bases of their columns have come 

 into mutual contact and have acquired a polygonal form. These latter were bred 

 in an aquarium. Similar clusters were found by Thomson attached to the inner 

 surface of a dead valve of Modiola modiolus. 



In pentacrinoid larvae somewhat older than the oldest examined by Seeliger 

 Doctor Carpenter found beginning immediately within the mouth a series of 

 irregularly lobed glandular masses, pale yellowish brown in color, projecting 

 into the cavity of the stomach and curving in an irregular spiral down to the 

 bottom of the cup. These glandular folds are richly clothed with long vibratile 

 cilia. The merest film of sarcode separates their secretion from the stomach 

 cavity. The slightest touch, even of a hair, ruptures them and causes the effusion 

 of a multitude of minute granules, some colorless and transparent and others of 

 a yellow or brownish hue. Carpenter believes that from their position and color 

 there can be little doubt that these lobes form a rudimentary lever. They appear 

 very early in the pentacrinoid, coloring the lower portions of its body in the 



142140 21 Bull. 82 34 



