Introduction to Animal Morphology. 243 



margined by a crown of large, simple, or clustered 

 cilia, sometimes bilobed, with an anterior and posterior 

 median notch, or divided into four or more tentacle- 

 like lobes, which may have ciliary girdles. This is a 

 form of the primary ciliary crown of the larvse of 

 Vermes, like the lophophore of Polyzoa. A fold of 

 integument at each side of the body is called the 

 mantle, and may be single and continuous, or of two 

 lateral, united, or separate lobes ; it may be present 

 in the embryo, and lost as age advances, or may be 

 absent. The mantle lobes are probably homologous 

 with the basal papillae of the notopodia, and between 

 them on the ventral surface the dermal and muscular 

 wall is developed into a thick process or foot, the chief 

 organ of progression, which may have a flat sole or a 

 sharp edge, and may be rudimental in sessile forms 

 (oysters, &c.) As this is the ventral surface of two or 

 three united metameres, it may be divided into two or 

 three parts, named, respectively, pro-, meso-, and 

 meta-podium ; sometimes it is longitudinally divided 

 into a middle and two lateral parts. The relation 

 between the foot and the under surface of the ordinary 

 body wall of a worm is shown by the fact that the 

 viscera are often prolonged into, and lie above it ; its 

 upper surface may develop an appendix or epipodium. 

 When the mantle is present it usually secretes a 

 shell,* more or less completely enclosing the body ; 

 in its simplest form this is a single lamina on the 

 mantle surface [univalve], or when the mantle is bi- 

 lobed it consists of two plates united dorsally by a 

 hinge, and is called a bivalve. The first form may be 



* Composed of Conchiolin 0.04, Calcium Carbonate 0.94, Calcium 

 Phosphate, Alumina, Iron, and Sihca, 0.02 = i .00. 



R 2 



