14 EMBEYOLOGICAL MONOGRAPHS. 



14'-19. Amphiura squamata. From Hubeit Lmlwig, Ziir Entwickelungsgeschicte des Ophiureiiskelettes, 1882 

 (Morphol. Studitu, II., Heft 2). Zeits. f. Wiss. Zool., XXXVI., PI. XI. 



^1, ^2- First and second auibulacral plates. B a. Radials of the young ophiuran. 



A d^ A d.,, A d3, etc. First, second, third, etc. ad- 7'. Tei-minal plates, 



anibulacral plates. To. Torus angularis. 



C. Dorsocentral plate. t. Teeth. 



in. Madreporio i)late. V V- Ventral plates. 



0. Oral plates (mouth shields). x. Remnant of embryonic skeleton. 

 11. Primary radials. 



14'. Young .Vmpluura, seen from tin- dorjal side. The composition of the plates, of i/-sliaped rods, is still plainly 

 visible. 



15. Somewhat older stage, seen from the actinal side. V, oldest ventral plate ; P, very young ventral plate ; 



t, rudimentary teeth. 



16. Somewhat older tliau fig. 14', but younger than fig. 15, seen from the dorsal side. 



17. Somewhat older than the stage corresponding to fig. 19, seen from the dorsal side, showing the arrangement 



of the intermediate plates formed between the central and the primary radials. 



18. Somewhat older than the stage of fig. 17, seen from the dorsal side ; the intermediate plates have greatly in- 



creased in size and number. 

 18'. Shows the arrangement of the plates of the actinal side in a stage slightly older than fig. 17. 



19. Stage corresponding to fig. 15, seen from the dorsal side ; intermediate plates begin to appear between the 



central plates and the primary railials. 



20-2.3. Ophioplwlis (?) and A.nphiara { !). From Alexander Agassiz, On the Embryology of Echinoderms. Mem. 



Am. Acad., IX., figs. 29, 31-33, 1864. 



20. Ophiopholiihc'Us> From a drawing made under the direction of L. Agassiz in 1849. Abactinal view of a 



young Ophiopholis to show the arrangement of the plates of the disk. 

 21-23. Anijihiura? 



21. A full-grown Plutens, in wliii-h the water-tubes, w, ?»', are plainly seen, d, digestive cavity ; m, mouth : 



a, anus ; t, rudimentiu-y tentacular lobes of the water-system ; %■', anal, and t', oral vibratile cord ; 

 c'-e*, arms of the Pluteus. 



22. Older stage, seen from the abactinal side, in which the arms of the Pluteus (c"-c<) are almost entirely resorbed ; 



the two long anns <•' are still intact, they are omitted for want of space, r, abactinal region ; ij, rudi- 

 mentary terminal plate ; y', adambnlacral plate ; »-^, junction of limestone rods of the long arms c'. 



23. The same, seen from the actinal side ; lettering as above : s, actinal region ; t, t!, tentacular loops. 



24. 25. Ophiocorna rosula. From T. H. Stewart, On the Yonng State of Ophiocoma rosula, and on the Form and 



Development of the Spines of this Species. Ann. k Mag. Nat. Hist., XVIII., 1856, PI. XV. 



24. Young Ophiocoma seen from the abactinal side. 



25. Actinal view of central portion of the disk. 



26-31. Amphiura squamata. From Max Schultze, Ueber die Entwickelung von Ophioh-pis s(iuamata, einerleben- 

 diggebaliri^nden Opldure. Arcliiv. f. Anat. Phys. u. Wiss. Med., 1S52, PI. I. 



26. Ovarian eggs of Amphiura squamata. 



27. Young embryo with rudiment.iry provisional limestone rods. 



28. Somewhat oMerthan fig. 27, the embryonic limestone rods are arranged symmetrically. 



29. Older embryo. In addition to the provisional limestone rods, a, we have also the radials, h, developed ; and 



the first trace of the terminal plates, <-. 



30. Tlie embryo has assumed a pentagonal outline ; of the provisional limestone rods we find only the remnants at 



a ; lettering as before ; the plates of the abactinal side are seen through from the ventral side under the 

 rudimentary actinal plates. 



31. Portion of a yonng Amphiura measuring J'" in diameter, seen from the actinal side : a, interbrachial dorsal 



plates ; h c, actinal plates adjoining actinostome ; d d, interbrachial plates of the actinal side ; c e, spoon- 

 shaped brachial plates; /, tcnninal plates; g, g, tentacles ; h, teeth. 



32. 33. Viviparoun Ophiuran. From August Krohn, Ueber einen neuen Entwickclungsmodus der Ophiuren. 



Archiv. f. Anat. Phys. u. Wiss. Med., 1857, PI. XIV. B. 



32. Actinal view of ophiuran embryo ; a, pentagonal disk of young ophiuran ; b, central cavity, the future 



mouth ; c, tentacles ; rf, tentacles of actinostome ; c, remnant of rudimentary Pluteus. 



33. Young ophiuran of same emliiyo ; a, dorsal plates ; b, arm plates ; c, terminal jdate ; d, spines of the actinal 



side projecting beyond the disk. 



