1 3 6 Introduction to A nimal Morphology. 



vesicles may be simple or divided into 2-7 smaller vesicles 

 (A. aurantiacus), whose ducts, however, miite, so that there 

 are never more than five openings. Right and left of each 

 vesicle opens one of the ten spherical, hollow, grape-like 

 bodies appended to the canal (Otocysts of Baur, but more 

 likely the homologues of the oral tentacles of Ophiuridae). 

 Respiratory organs may exist on the dorsal surface as rounded 

 or conical foot-like skin-processes, communicating with the 

 body cavity (skin gills). In Solaster, the sea-water can enter 

 the body by inter-brachial cribriform plates, pierced by the 

 ducts of the genital glands. 



The vascular system has its two rings and heart ; when 

 there are several sand canals, there are as many hearts, and the 

 septum containing the heart is double the size of any of the 

 other radial mesenteries. The anal ring is wide, pierces all 

 the septa, and receives a genital vein on each side of each 

 partition. The oral ring is narrower, more muscular, and lies 

 under the nerve, and over the water-vascular ring. Under 

 each angle of the mouth a vessel passes to each arm, and five 

 branches are distributed to the stomach. The blood in the 

 oral ring is yellow-brown, in the anal whitish. 



Genital glands, each consisting of one (Ctenodiscus) or 

 many grape-like masses, lie in pairs on both sides of the 

 septa, even to the tip of the arm ; in Astropecten these are 

 numerous, and extend into the disc ; in Llwydia, several 

 thousand glomeruli are scattered along the whole arm. Each 

 Astropecten may produce half a million eggs. The eggs in 

 some are developed directly (Echinaster, Asteracanthion 

 Miilleri ; in Pteraster they develop in a dorsal brood sac, 

 with a narrow neck placed between the paxillated membrane 

 and the skeleton) ; but more commonly there is a larval stage, 

 which may be possibly be one of three kinds: — ist. Bipin- 

 naria — bilaterally symmetrical, skeletonless, flat, smaller at 

 one end, and with lanceolate lappets along the margin. The 

 rudimentary water-vascular rosette has swollen MUllerian ap- 

 pendages, and the stomach is formed in the protoplasm by 

 invagination (Solaster, Asteracanthion). 2nd. Brachiolaria — 

 with three warted arms anteriorly. 3rd. A worm-like larva of 

 four metameroid segments, which, speedily losing its seg- 



