DEVELOPMENTAL HISTORY OF THE MOLLUSCA. 37 
dry. Detached portion of the residual yelk concerned in the formation of the renal organ. 
v. Descending border of the yelum. 
ep. Epiblast or ectoderm. 
f. Foot. 
hy. Hypoblast or endoderm. 
ime. Darmfaserblatt, or alimentary layer of mesoblast. 
int. Intestine. 
int’. Terminal portion of the intestine. 
m, m'. Retractor muscles. 
me. Mesoblast. 
mn. Mantle rudiment. 
ng. Nerve-ganglion. 
ng’, ng". Secondary ganglionic masses (? pedal ganglion). 
o. Mouth. 
o'. Thickening which precedes the mouth. 
a. CEsophagus. 
ot. Orifice of invagination (blastopore). 
op. Operculum. 
ot. Otocyst. 
pg. Pigment-vesicles of unknown function. 
ph. Pharynx. 
pl. Plug of the shell-gland or groove. 
pme. Hautfaserblatt, or tegumentary (parietal) layer of the mesoblast. 
g. Dark-coloured cell-mass of unknown significance. 
R. Richtungsblaschen, or particles extruded from the cleaving egg-cell, frequently 
recognizable as the remains of the germinal vesicle. 
ry. Residual yelk. 
sh. Shell. 
shgr. Shell-grooye, or follicle of the shell-gland. 
shp. Shell-patch, or primitive shell-secreting area. 
x. Undifferentiated cells of the colourless (or segregate) yelk, enclosed by the epiblast. 
In Plate 7. figs. 4, 5, 8, 11, the letter 2 is applied to a deep-lying dark-looking 
mass of cells which lies between the two coloured residual yelk-spheres. 
