DEVELOPMENT OF GASTROPODS. 243, 
tle on the left side of the body behind the head. In a large 
Lunatia it isan inch long, with a vein at the base, the gill- 
lobes arranged like the teeth in a comb. <A smaller, much 
narrower gill lies within and parallel to it. The ovary is 
situated near the stomach, the ovi- 
duct ending near the vent. 
The eggs are laid in capsules (Fig. 
185, Purpura lapillus and two egg- 
capsules) of varied form attached 
to rocks or, as in Zrochus and the 
Nudibranchs, in masses of jelly at- “ 
tached. to sea-weeds or stones. tice ta tee cue aee 
As a type of the mode of devel- After Morse. 
opment of Gastropods may be cited that of Calyptrea si- 
nensis, represented in our waters by Calyptrea striata Say 
(Fig. 186). 
Vv 
Fig. 188, 
Fig. 186.—Calyptrea striata, natural size.—After Morse. 
Fig. 187.—Veliger of Calyptrea. f,foot; v, velum ; m, mouth; ce, ectoderm ; ‘ve, 
mesoderm.-—After Salensky. 
Fig. 188.—Veliger of Culyptrea further advanced. m, mantle ; v, velum ; 7, foots 
h, larval heart ; », permanent ; 4, primitive kidney ; s, crosses the shell and rests or 
the yolk.—After Salensky. 
According to Salensky, after segmentation of the yolk 
into eight cells the first four cells or ‘spheres of segmenta- 
tion” subdivide, enclosing the yolk-mass, and constituting 
the ectoderm or outer germ-layer, the yolk-mass forming the. 
endoderm. The cells of the outer germ-layer multiply and. 
form the blastoderm, from which the skin, mantle, and ex- 
ternal organs, as well as the walls of the mouth, arise. The: 
“primitive” mouth of the gastrula is formed by the invagi-. 
