THE DEVELOPMENT OP ASTBRINA GIBBOSA. 283 



on prseoral lobe for attacbment of larva, gen. r. Genital rachis. gob. Goblet 

 cells, hist. Involution of ectoderm to facilitate bistolysis. Ihy. Left water- 

 vascular rudiment or hydroccele ; its lobes are numbered with Arabic numerals. 

 Roman numerals i, ii, iii, iv, v, denote t.lie arm rudiments, lo, larval organ. 

 Ice. larval oesophagus. Ipc. Left posterior coelom. I'p'c . The right ventral 

 horn of the same. l"p"d'. The right dorsal horn of the same, l.stom. 

 Larval stomach, mes. Mesenchyme, mp. Madreporic pore. muse. Muscular 

 tissue, muse. amb. Ambulacral muscles, muse. law. Larval muscles, muse, 

 retr. Retractor muscles of adult oesophagus or stomach, nerv. Nervous tissue. 

 nerv. eirc. The nerve-ring. nerv. larv. Larval nervous tissue, or. e. Oral 

 coelom. pbr. Peribranchial space, p. c. Pore-canal, p'd. Additional pore- 

 canal in abnormal larva, per. Peritoneum, ph. Perihaemal space. The 

 perihsemal rudiments are numbered 1.2, 2.3, 3.4, 4.5, and 5.1, according as 

 they originate between the hydroccele lobes 1 and 2, 2 and 3, 3 and 4, 4 and 5, 

 and 5 and 1 respectively, pr.germ. Primitive germ cells, pr.germ.inv. Invo- 

 lution of the peritoneum whence these cells arise, py. Pyloric sac and its 

 caeca, ret. Retinal cells, rhy. Right hydroccele. Its lobes when they exist 

 are numbered like those of the left hydroccele, &c. r'hy'. Extra right hydroccele 

 present in abnormal larva, rpe. Right posterior coelom. sang. circ. Oral 

 blood-ring. stc. Stone-canal, st'e'. Extra stone-canal present in abnormal 

 larva. T. Terminal plate, tr. Trabecula. vit. Cells forming crystalline 

 body (Glaskorper). wv. Radial water-vascular canal, wvr. Water-vascular 

 ring-canal. 



PLATE XI. 



All the figures are reproduced, though in a somewhat simplified form, from 

 Ludwig's memoir on the development of Asterina gibbosa. The various 

 figures have, however, been enlarged or reduced as the case demanded so as to 

 bring them to one uniform scale of magnification, viz. 85 diameters. 



Fig. 1. — A gastrula with wide blastopore. Stage A. This stage is reached 

 on the second day. 



Fig. 2. — A slightly older gastrula. The blastopore is commencing to be 

 narrowed, and one of its lips is reflected over it. 



EiG. 3. — A still older gastrula. 



Fig. 4. — Lateral view of larva three days old which has just escaped from 

 the egg membrane. The "larval organ" (/. o.) or prseoral ridge of ectoderm 

 with long cilia has appeared. Stage B. 



Fig. 5. — Ventral view of the same larva. 



Fig. 6. — Dorsal view of the same larva. 



Fig. 7. — Lateral view of larva of six days. The disc for adhesion {fix.) has 

 appeared in the centre of the larval organ. Stage C. 



Fig. 8. — Antero-lateral view of the same larva of six days. 



