136 Introduction to Animal Morphology. 



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

 (A. aurantiacus), whose ducts, however, unite, 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 



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 m< . The anal ring is wide, pien 



j>ta, and receives a genital vein on each si 

 partition. Tin- oral ring is narrower, more muscular, and lies 

 under the nerve, and over the wah r-va^cular ring. I'nder 

 cadi an-le of the mouth a \. h arm, and five 



branches are distributed to the stomach. The blood in the 

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



(u-nital glands, each consisting of one (Ctenodiscus) or 

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

 . even to the tip of the arm ; in Astropecten these are 

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

 thousand glomeruli are scattered along the whole arm. 

 Astropecten may produce half a million eggs. The CL 

 some are developed directly (Echinaster, Asteracanthion 

 Mulleri ; 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 

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

 naria bilaterally symmetrical, skeletonless, flat, smal' 

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

 rudimentary water-vascular rosette has swollen Miillerian ap- 

 pendages, and the stomach is formed in the protoplasm by 

 imagination (Solaster, Asteracanthion). 2nd. Brachiolaria 

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

 four metameroid segments, which, speedily losing its seg- 



