MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 99 



7. KROIIN, A. " Uobcr eineu neuen Entwiekeluugsinodus der Ophiuren." Mueller's Archiv. f. Anat. u. Phys., 1857, 

 p. 369. 



8. LYMAN, T. " Ophinra broviepina Say." Pt. I. 111. Cat. Mus. Comp. Zool., Harvard Coll. 1865, p. 16. 



9. LYMAX, T. " Report on the Ophiuridse." Vol. V. Challenger Report. 



10. MeBiiiDE, E. W. " The Development of ABterinagibbosa." Q. J.Mic. Sc., vol. 38. 



11. FRKYER, \V. " Ueber die Bewegungen der Seesterne.'' MittU. a. d. Zool. Stat. z. Neapel. den. 1886. 



12. SAY, T. "Ophiura brevispinn," Journal Phil. Acad., Vol. V. 1825. Page 149. 



13. SEMON, R. ' Die Entwickelnng derSyuaptadigitataunddieStamniesgeschicliteder Echiuodermeu." Jonaisch. 

 Zeitschr. f. Naturwiss. 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 enterocojle. 



aer Eight anterior entorociule. 



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 enteroctcle. 



et , End tentacle. 



he Canal connecting posterior en- 

 teroctcle and hydroca'le. 



he Hypogastric euteroecele. 



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

 gastric enteroccele. 



hy Hydroccele. 



ips Inner perihsemal sinus. 



ipax 51 Interradial pouch of axial sinus. 



lo Larval organ. 



m Mouth. 



mes Mesenchyme. 



ill First pair tentacle nerves. 



nr Nerve ring. 



oe (Esophagus. 



od Oral disk. 



opr Outer perihtemal ring. 



pc Pore canal. 



pe Posterior enterocoeles. 



pv Poliau vesicle. 



rad 11 Radial nerves. 



rg Radial grooves. 



rps Radial perihsemal space. 



sin a Sinus "a". 



sinb Sinus "b". 



8t Stone canal. 



88 Subneural sinus. 



8 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. 



