THE DEVELOPMENT OF ASTERINA GIBBOSA. 401 
tissue. musc.amb. Ambulacral muscles. muse. /arv. Larval muscles. muse. 
retr. Retractor musclesof adult cesophagus or stomach. xerv. Nervous tissue. 
nerv. circ. The nerve-ring, zerv. darv. Larval nervous tissue. or. c. Oral 
ccelom. pdr. Peribranchial space. p.c. Pore-canal. p’'c’. Additional pore- 
canal in abnormal larva. yer. Peritoneum. pf. Perihemal space. The 
perihemal 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 Lrespectively. pr. germ. Primitive germ cells. pr. germ. inv. Invo- 
lution of the peritoneum whence these cells arise. py. Pyloric sac and its 
ceca. vet. Retinal cells. shy. Right hydrocele. Its lobes when they exist 
are numbered like those of the left hydroccele, &c. r’Ay'. Extra right hydroccele 
present in abnormal larva. spe. Right posterior celom. sazg. cire. Oral 
blood-ring. séec. Stone-canal. sé/c’. Extra stone-canal present in abnormal 
larva. 7. Terminal plate. ¢7. Trabecula.  vi¢. Cells forming crystalline 
body (Glaskorper). wv. Radial water-vascular canal. wor. Water-vascular 
ring-canal. . 
PLATE 18. 
All the figures are reproduced, though ina 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. 
Fic. 1.—A gastrula with wide blastopore. Stage A. This stage is reached 
on the second day. 
Fie, 2.—A slightly older gastrula. The blastopore is commencing to be 
narrowed, and one of its lips is reflected over it. 
Fig. 3.—A still older gastrula. 
Fic. 4,—Lateral view of larva three days old which has just escaped from 
the egg membrane. The “larval organ” (/. 0.) or preoral ridge of ectoderm 
with long cilia has appeared. Stage B. 
Fie. 5.—Ventral view of the same larva. 
Fie. 6.—Dorsal view of the same larva. 
Fic. 7.—Lateral view of larva of six days. The disc for adhesion (/iz.) has 
appeared in the centre of the larval organ. Stage C. 
Fig. 8.—Antero-lateral view of the same larva of six days. 
Fie. 9.—Anterior view of the same larva of six days. 
Fie. 10.—Left view of fully developed larva of seven days. Stage D. 
Fic. 11.—The same drawn in the position it assumes in life. 
Fic. 12.—Left view of larva in which metamorphosis has commenced, and 
which has fixed itself. The Arabic figures denote the primary lobes of the 
water-vascular system or hydroccele, the Roman figures the rudiments of the 
arms. The larval organ has disappeared. Stage H. 
