346 Prof. E. W. MacBride. The Artificial Production of 



(15) MetschnikofF, E., " Studien iibei- die Entwicklung der Echinodermen und Nemer- 



tinen," ' Mem. de I'Academie Imp. de St. Petersbourg,' vol. 14 (1869;. 



(16) Miiller, Job., " Ueber die Larvenzustande und die Metamorphose der Opbiuren 



und Seeigel," 'Abb. Konig. Akad. Wiss., Berbn,' 1846. 



(17) Shearer, de Morgan and Fachs, " On the Experimental Hybridisation of Echinoids," 



' Phil. Trans.; B, vol. 204 (1914). 



(18) Von Ubisch, L., " Die Entwicklung von Strongylocentrotus lividus {Echinus micro- 



tuberculatus, Arhacia pustulosa)," 'Zeit. Wiss. Zool.,' vol. 106 (1913). 



EXPLANATION OF PLATES. 

 List of Abbreviations. 



ab.t., aberrant tentacle, i.e., lobe of the right hydrocele which projects into the 

 blastocoele and not into the amniotic cavity ; a.l., antero-lateral ciliated arm ; am., 

 amniotic cavity ; an., anus ; ax., axial sinus ; as'., axial sinus developed on the right 

 side from the right anterior ccelom ; calc, calcareous plate ; ciL, portions of the ciliated 

 band of the larva forming the loop within which the amniotic invagination is formed 

 both on the right and on the left side ; coe., crelom ; d.a., dorsal arch, i.e., the calcareous 

 rod lying above the oesophagus in the larva ; d.c.ep., dorsal ciliated epaulette ; d.s., 

 dental sac associated with the left hydrocoele ; d.s'., dental sac associated with the right 

 hydrocoele ; Ech., Echinus-rudiment ; int., intestine ; l.a.c, left anterior coelom ; l.hy., 

 left hydrocoele ; Lp.c, left posterior ccelom ; l.sp., left group of spines within the ciliated 

 loop ; I'.sp'., left spine outside the ciliated loop ; mad., madreporite ; m.p., madreporic 

 pore ; m'.p'., additional madreporic pore ; m.sp., madreporic spine ; oes., oesophagus ; 

 p.c., pore canal ; p'.c'., additional pore canal ; p.d., postero-dorsal ciliated arm ; ped., 

 pedicellaria ; p.o., post-oral ciliated arm ; p):o., prae-oral ciliated arm ; r.a.c, right 

 anterior coelom ; r./iy., right hydrocoele ; r.p.c, right posterior cnelom ; 7:sp., right group 

 of spines within the ciliated loop ; r'.sp'., right spine outside the ciliated loop : sept.y 

 remains of the septum which formerly divided right and left axial sinuses from one 

 another ; st.c, stone-canal ; .si. 'c'., additional stone-canal on the right side ; st".c"., additional 

 stone-canal on the left side ; stoyn., stomach ; o.c.ep., ventral ciliated epaulette. 



N.B. — Skeletal structures are indicated in the drawings of whole larvee by heavy 

 black lines. 



Plate 4. 



Fig. 1. — Young larva between three and four days old viewed from the ventral aspect. 



Preserved in osmic acid, followed by Muller's fluid, which has dissolved 

 the skeleton. Magnification 330 diameters. Note the stomodpeum just about 

 to open into the oesophagus {ces.). Only the post-oral ciliated arms are 

 developed {p.o.). This larva is approximately at the stage of development at 

 which larvJB were transferred to hypertonic water in 1914, 1915 and 1916, 

 and a little younger than that at which they were transferred to this water 

 in 1917. 



fig. 2. — Larva 12 days old viewed from the dorsal aspect, showing on the left side the 

 ■ formation of the hydrocoele and on the right side the almost completed 

 separation of the coelomie sac into anterior and posteiior portions. 



Drawn from life from the cultures of 1914. Magnification 90 diameters. 

 This larva is about the stage of development at which, in 1917, larvce were 

 transferred from hypertonic water to normal water in the plunger jar. 



