640 MR. H. G. NEWTU ON THE 



(7) LuDWiG, H. (1891). — " Znr Entwickelungsgescliichte cler 



Holothurieu,'' Berlin, Sitzungsb. Akad. Wiss. no. 10, 

 pp. 179-192 ; and (zweite Mittheilung), ibid. no. 32, 

 pp. 603-612. 



(8) MacBkide, E. W. (1912).— "On a Collection of yonng 



Holothurioids," National Antarctic Expedition Nat. Hist. 

 1901-1904, vol. vi. pp. 1-9, pis. 1 & 2. 



(9) MacBride, E. W., & J. C. Simpson (1908).— "Ecliinoderin 



Larvse," ibid. vol. iv. pp. 1-9, one plate. 



(10) Masterman, a. T. (1902). — "The Early Development of 



Cribrella oculata Forbes, with Remarks on Ecliinoderni 

 Development," Trans. E.. Soc. Edinb. voLxl. pp. 373-417, 

 pis. 1-5. 



(11) Selenka, E. (1876).—" Zur Entwickelung der Holotlivirien," 



Zeit. Wiss. Z. Leipzig, vol. xxvii. pp. 155-188, pis. 9-13. 



(12) Semon, R. (1888). — " Die Entwickelung von Synapta digl- 



tata" Jena Zeit. Naturw. Bd. xxii. pp. 175-309, pis. 6-12. 



EXPLANATION OF THE PLATES.l 



Lettering. 



A., anterior ; a., anus ; Ae., archenteron ; a + k., anterior coeloiii plws hydrocoel ; 

 bl., blastopore ; blc, blastocoel ; D., dorsal ; d. (following the abbreviation for a radial 

 canal), tentacle projecting dorsalwards from the radial canal indicated ; ect., ectoderm ; 

 e.m., egg-membrane; ep.n., epiueural space; f.j., follicular jelly; g., gut; L., left; 

 iD., left dorsal radial canal; LV.,\eit ventral radial canal; ?»es., mesenchyme ; 

 mp.'p., madreporic pore; MV., mid-ventral radial canal ; MVl. and MVr., primary 

 tentacles developed to the left and right, respectively, of the 3IV. canal ; MVlp. 

 and MVr p., first pair of podia developed from the left and right sides, i-espectively, 

 of the iHX^. canal ; P., posterior; p. i>., polar bod}-; p.c, posterior coelom ; p.o.l., 

 prse-oral lobe ; P.v., Polian vesicle ; R., right ; BD., right dorsal radial canal ; 

 r.n., radial nerve; BV., right ventral radial canal ; s.c, stone-canal; Sp., si)eniiato- 

 zoon ; Stom., stomodieum (oral atrium) ; t., tentacle ; V., ventral ; v. (following the 

 abbreviation for a radial canal), tentacle projecting ventralwards from the radial 

 canal indicated j tv.v.r., ring-canal of the water- vascular sj'stem. 



PXAIE I. 



Fig. 1. Cucumaria normani. Unfertilized egg seen from the side. 



2. C normani. Animal pole of the same egg. Leitz. obj. 6, oc. 3. 



3. C. normani. Four-cell stage. 



4. C. normani. Earl}' morula seen from above. 



5. C. nonnani. Section through the wrinkled blastula, showing at + a 



cytoplasmic inclusion. Leitz obj. 6, oc. 3. 



6. C. saxicola. Fourth-daj' larva, drawn from a preserved specimen. The 



tentacles are withdrawn within the stomoda;uni, and two of their tips 

 only can be seen. Note the position of the stomodaeum on the left side 

 of the larva. 



7. C, normani. Longitudinal (? coronal) section through the fulli'-formed 



gastrula. The cavity of the archenteron is encroached upon at * by the 

 inflected middle part of one of its flattened walls. 



8. C. normani. Longitudinal (? sagittal) section of a free-swimming larva 



44 hours old, showing the tjrst stage in the segmentation of the coelom. 



