408 E. W. MACBRIDE. 
rudiment is at one point attached to the oral wall of the axial sinus. 
(Compare Plate 25, fig. 110.) 
Figs. 104—106. Three sections of a young star-fish, in which R equals 
‘4 millimetre. Fig. 104 shows the primitive germ cells arising from 
the involution of the peritoneum. Figs. 105 and 106 show that they now 
extend throughout the whole extent of the ovoid gland; these figures 
also show the relation of the oral end of the axial sinus to the peri- 
heemal spaces. 
Fics. 107 and 108.—Two sections from same series as Figs. 82—84, 
magnified 350 diameters. They show the development of the oral “blood ” 
ring, sazg. cire., aS a modification of the mesenchymatous tissue of the 
blastoccele. id. Fibrous tissue. 
Fie. 109.—Similar section of a young star-fish, in which R equals °45 
millimetre. Same magnification. The blood-ring is fully formed. Notice 
also the minute cells amongst the nerve-fibres (dip. gang.). 
PLATE 25. 
Fic. 110.—Longitudinal section of the stone-canal of young star-fish, in 
which R equals ‘8 millimetre. sang. cire. Oral “blood” ring. wvr. Water- 
vascular ring-canal. musc. amb. Muscles of ambulacral ossicles. Notice the 
incipient division of madreporic pore into two, and entire independence of 
ovoid gland and blood-ring. Magnified 350 diameters. 
Fic. 111.—Diagram showing the relative positions of the ovoid gland, 
stone-canal, and various sinuses in proximity. gez. 7. Genital rachis. ad, 
Aboral sinus (or sizus a.). pr. germ. inv. Primary peritoneal involution to 
form germ cells. The cavity of this is probably the same as sizus 6 in next 
figure. The axial sizws a' is sinus c. The dotted lines show the continuity of 
two parts of the ovoid gland in a different plane to that of the stone-canal. 
Fic. 112.—Similar diagram of Amphiura squamata. Accompanying 
spaces, sinus a, sinus b, and sinus c, as in the author’s paper (14). 
Fies. 113—118 illustrate the development of the ovoid gland and genital 
rachis. They are all taken from sections cut parallel to the disc; they are, 
in fact, transverse sections of the interradial septum in which the axial sinus 
is embedded. 
Figs. 113 and 114. Two sections from a star-fish, in which R equals °45 
millimetre. Fig. 113 shows the manner in which the right hydro- 
ccele is enclosed in the upper part of ovoid gland; Fig. 114, the 
primitive peritoneal involution, the pore-canal, and the crescentic form 
of right hydroccele. Magnification 350 diameters. 
Figs. 115 and 116. Two sections from star-fish, in which R equals 
‘7 millimetre. ad. Aboral sinus containing the rudiment of genital 
rachis. Fig. 115 shows that the sinus is a portion of the celom 
shut off by the outgrowth of a flap from the body-wall. 
