THE DEYELOPMENT OP ASTERINA GIBBOSA. 291 



rachis. Jig. 115 shows that the sinus is a portion of the coelom 

 shut off by the outgrowth of a flap from the body-wall. 



Fig. 117. Section from star-flsh, in which R equals 2'2 millimetres, 

 showing the continuity of rachis and ovoid gland, and that the rachis 

 now extends in both directions. Magnified 150 diameters. 



Fig. 118. Section from star-fish, in which B, equals 3 millimetres, show- 

 ing fully developed ovoid gland and changed form of stone-canal. 

 Magnified 350 diameters. 



PLATE XIX. 



Figs. 119 — 121. — Portions of three sections from the same series as Fig. 

 118. Fig. 119 shows the genital rachis enclosed in the branch from the 

 aboral sinus, ab. Fig. 120 shows the passage of the genital rachis into the 

 rudimentary genital organ, and the outgrowth of septum which cuts off the 

 perihsemal space surrounding this rudiment from the " genital vessel." ab. A 

 branch of the aboral ring. Fig. 121 shows the development of the cavity of 

 the genital organ. Magnification 350 diameters. 



Pigs. 122 and 123. — Two sections of young ovaries, from a specimen in 

 which E, equals 3'7 millimetres. Fig. 122 shows the continuity of the ovary 

 and rachis, Fig. 123 the outgrowth of germ cells to form the genital duct. 



Fig. 124. — Portion of body-wall of gastrula figured in Plate 19, fig. 21. 

 Notice the absence of mesenchyme, end. Endoderm. Magnification 600 

 diameters. 



Fig. 125. — Similar view of the body-wall of slightly older embryo, to show 

 the formation of mesenchyme. Same magnification. 



Fig. 126. — Portion of the gut epithelium of larva figured in Plate 20, 

 figs. 51 — 53. Same magnification. 



Fig. 127. — Epithelium of the adult oesophagus of the larva shown in 

 Plate 22, fig. 76, Stage G. Magnified 480 diameters. 



Fig. 128. — Epithelium of the pyloric sac (larval stomach), from the same 

 section as foregoing. 



Fig. 129. — Epithelium of the lateral ,wall of the stomach of a star-fish, in 

 which R equals 8 millimetre. Magnified 480 diameters. 



Fig. 130. — Epithelium .ptalporal wall of the stomach from the same section 

 as foregoing. At X it passes into the epithelium of the pyloric sac. 



Figs. 131 and 132. — Epithelium of the pyloric sac and of the rectal caecum 

 respectively. From the same section as fig. 130. 



PLATE XX. 



Figs. 133 135.— Three sections of the ectoderm of the anterior surface 



of preeoral lobe of larva of Stage D. Fix. Disc for fixation. /. o. Larval 



