THE DEVELOPMENT OE ASTBEINA GIBBOSA. 283 



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

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

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

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

 Iw. larval oesophagus. Ipe. Left posterior coelom. Hp'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. Madreporio pore. muse. Muscular 

 tissue, muse. amb. Ambulaoral muscles, muse. larv. Larval muscles, muse, 

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

 nerv. cire. The nerve-ring. nerv. larv. Larval nervous tissue, or. c. Oral 

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

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

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

 they originate between the hydroooele lobes 1 and 2, 2 and 8, 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 

 C8eca. ret. Retinal cells, rhi/. Right hydrocoele. Its lobes when they exist 

 are numbered like those of the left hydrocoele, &c. r'A/. Extra right hydrocoele 

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

 blood-ring. ste. 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 XL 



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. 



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

 on the second day. 



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

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



Pig. 3.— A still older gastrula. 



jjQ_ 4_ Lateral view of larva three days old which has just escaped from 



the egg membrane. The « larval organ" {I. 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. 



Pig. 7.— Lateral view of larva of six days. The disc for adhesion (Js:.) has 

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



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



