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 p. 369. 



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EXPLANATION OF PLATES. 



The figures illustrating this paper were drawn to the same scale of magnification, 330 diameters, and were 

 reduced one-half in reproduction. 



Figs. 1, 2, 4, 6, 7, 9, 17, 31, and 32 were reconstructed from series of transverse and sagittal sections. 



In all cases the part of the figure which is nearest the top of the plate is either anterior or else ventral in the 

 larva. 



ABBREVIATIONS USED. 



ae l Loft anterior enteroecale. 



aer Eight anterior enterocoele. 



ap Apical plate. 



ax sin Axial Sinus. 



b Blastopore. 



cb 1,2, 3, and 4 Ciliated bands. 



eg Circular groove. 



cm Circular mesentery. 



cp Cellular plug. 



d Dorsal pore. 



ee Epigastric euterocojle. 



et End tentacle. 



he Canal connecting posterior en- 



terocuole and hydrocuile. 



he Hypogastric enterocoele. 



hip 1-2,2-3,3-4,4-5 Interradial pouches of the hypo- 

 gastric enteroccele. 



hy Hydrocffile. 



ips Inner perih;emal sinus. 



ipax 51 Interradial pouch of axial sinus. 



lo Larval organ. 



m Mouth. 



nies Mesenchyme. 



ill First, pair tentacle nerves. 



iir Nerve ring. 



oe (Esophagus. 



od Oral disk. 



opr Outer perihsemal ring. 



pc Pore canal. 



pe Posterior enterocooles. 



pv . Polian vesicle. 



rad n Eadial nerves. 



rg Eadial grooves. 



rps Eadial perihremal space. 



sin a Sinus "a". 



sinb Sinus "b". 



at Stone canal. 



ss Subneural sinus. 



s Stomach. 



tl First pair foot tentacles. 



t2 - Buccal tentacles. 



wvr Water vascular ring. 



I, II, III, IV, V Arm rudiments. 



1,2,3,4,5 Eadial water canals. 



