MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 99 



7. Krohn, A. " Uober einen neuen Entwickelungsmodus der Ophiuren." Mueller's Archiv. f. Anat. u. Phys., 1857, 

 p. 369. 



8. Lyman, T. " Ophiura brevispina Say." Pt. I. 111. Cat. Mus. Comp. Zool., Harvard Coll. 18G5, p. 1(5. 



9. Lyman, T. " Report on the OphinridsB." Vol. V. Challenger Report. 



10. McBridb, E. W. "The Development of Asterina gibbosa." Q. J. Mic. Sc, vol. 38. 



11. Prkyei:, W. " Ueber die Bewegungen der Seesterne." Mitth. a. d. Zool. Stat. ■/,. Neapel. dec. 1886. 



12. Sat, T. " Ophiura brevispina." Journal Phil. Acad., Vol. V. 1825. Page 119. 



13. Semon, B. "Die Entwickolung dorSynaptadigitataunddieStammcsgeschichtoder Echinoderinou." Jenaisch. 

 Zeitschr. f. Natnrwiss. XXII. 1888. 



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. 



ael Left anterior enteroccele. 



aer Right anterior enterociele. 



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 enteroccele. 



et End tentacle. 



he Canal connecting posterior en- 



terocicle and hydroccide. 



he Hypogastric enteroccele. 



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

 gastric enteroeoele. 



hy Hydrocccle. 



ips Inner perihsernal sinus. 



ipax 5 1 Interradial pouch of axial sinus. 



lo Larval organ. 



m Mouth. 



mes Mesenchyme. 



nl First pair tentacle nerves. 



nr ... Nerve ring. 



oe .. Oesophagus. 



od .. Oral disk. 



opr .. Outer perihsemal ring. 



pc .... Pore canal. 



pe ... Posterior enterocceles. 



pv Poliau vesicle. 



rad n Radial nerves. 



rg Radial grooves. 



rps Radial perih;emal space. 



sin a Sinus "a". 



sin b Sinus " b ". 



st 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 Radial water canals. 



