THE DEVELOPMENT OF THE ASTERIDEA. 



481 



has pointed out that, in /iritit/iga endecacnemos, the genitalia 

 are numerous distinct glands, arranged in 1 \v<> series, one on 

 each side of the middle line of the central half of each ray. 

 Each of these ovaries or testes has a separate aperture. 



In some Star-fishes, as in some Holothurids, the embryo 

 passes into the Star-fish form \vithout any free larval stage. 

 But, more usually, an Echinopaedium is formed in the same 

 \vav as in the Holothurians, though it presents differences 

 in the arrangement of its ciliated bands, and especially in 

 their prolongation into numerous lobes or narrow processes, 

 as in the remarkable form originally named JSipinnaria. 

 (Fig. 135, D D', and Fig. 138). It has no calcareous skel- 

 eton. 



FIG. 188. A young Asterid larva (Bipinnana. after Muller). A, ventral, B, lateral, 

 vie VB of larva (Bipinnarla). C, Bipinnaria with rudiment of the Star-fish: a, 

 mouth ; A, oesophagus ; c. stomach : <'. ir.tcsiinc : o, aims; #, veuiral. y. dorsal, 

 side 1 of til. 1 anterior end of the bo<iy ; (I, d', ciliated hand* : A, caecal d;\vni< uliiiu 

 forminir the rudiment of the amhnlacral vascular system, and opi:niiir externally 

 by the pore g. 



According to the observations of Prof. A. Agassiz, 1 which 

 have been confirmed by Metsclmikoff and Greef, the ambu- 

 lacral vessels commence as diverticula of the stomach, which, 

 becoming detached from the alimentary canal, give rise to the 

 peritoneal cavity, and to all the substance of the body be- 

 tween the endoderm and the ectoderm. 2 A portion of one of 

 these diverticula, however, separates itself from the rest, 



1 " Embryology of the Star-fish." (" Contributions to the Natural History 

 of tho IViti'*l stnti-s," v., 18C4.) The species, the development of which is 

 described in this important memoir, are Asteracanthion pallidus and A. bery- 

 liit n*. 



a Probably independently-developed mesoblastic cells contribute to the 

 formation of the mesoderm/as in the Holothurids. 



21 



