BRACHIOPODA 171 
whole animal is about 2°5 mm. long, and about the same 
in breadth. 
The shells are secreted by the body-wall or by the 
mantle. Since the body les chiefly in the dorsal shell, the 
larger part of the latter is secreted by the body-wall, and the 
dorsal mantle is of small extent; on the other hand, the 
greater part of the ventral shell is lined by a fold of integu- 
ment, the ventral mantle. 
The substance of the shell is composed of minute calcare- 
ous spicules kept together by a network of organic fibrils 
(Fig. 107). The shell is pierced by numerous canals, whose 
outer ends are somewhat enlarged and covered with a cuticle. 
Since the mantle is formed of a duplicature of the body- 
wall, it is necessarily double, and the body-cavity extends into 
it, in some places this space lodges the reproductive organs. 
The mantle sends a prolongation into each of the canals in the 
shell, which is continuous with some of its blood-vessels. These 
prolongations contain blood- 
corpuscles, and doubtless 
serve to nourish the organic 
fibrils which keep together 
the calcareous spicules of 
the shell. The lophophore 
occupies a considerable part 
of the dorsal shell, and forms 
a large part of the body- 
wall. Its shape is oval, its 
border running parallel to 
the edge of the shell, except 
at the anterior median line, ; a 
where a narrow deep in- Last 
Fic. 108.—Waldheimia flavescens. Interior 
dentation almost divides it of dorsal valve, to show the position of the 
into two, and thus gives lophophore. A portion of the fringe of 
: cirrhi has been removed to show the 
it a somewhat horse-shoe brachial membrane, and a portion of the 
shape. The indentation is spiral extremities of the arms. 
3 F : A. Position of mouth. 
occupied by a median ridge 
in the dorsal shell (Fig. 107). The lophophore carries 
round its edge, on the dorsal side of the mouth, from 
70 to 100 tentacles; at the base of the tentacles is a ciliated 
