150 THE ANATOMY OF AMPHIPTYCHES URNA. 
which in places appears to be “‘ running together” to form the shells enclosing the 
ova. x. Portions of the yellow-coloured material of varying size and shape ; sh. the 
same material, which has formed a definite “‘ shell” ; sh. the same material prior to 
the definite formation of a “ shell.” 
Fig. 3.—Transverse section across the body some little distance behind the 
proboscis, but anteriorly to any of the reproductive organs. c. Dense, somewhat 
homogeneous mass of consecutive tissue occupying the centre of the body; circ.1 outer 
layer of circularly disposed muscle fibres; circ.” inner layer of circularly disposed 
muscle fibres; cut. cuticle; dv. dorso-ventral muscle fibres; e. epidermic cells ; 
n. lateral nerve cord ; ne. excretory vessels lying in the central “‘ core’ of connective 
tissue; yk. yelk masses. 
Fig. 4.—Transverse section through the region of the sucker. cf. cut. cuticle ; 
ep. epidermis ; ik. spines protruding from the surface. 7. lateral nerve cords passing 
backwards from the transverse commissure at the anterior end of the sucker; ¢. 
testes ; yk. yelk masses. 
Fig. 5.—Transverse section through a spine, showing the concentric layers of 
which it is formed, and the special muscles attached to it. 
Fig. 6.—Longitudinal section through a spine, showing the point protruding 
through the cuticle, the concentric layers of which it is composed, and the special 
muscles concerned in its protrusion and retraction. 
Fig. 7.—Figures showing the development of the spines on the embryo. a. the 
youngest form ; d. the oldest. 
Fig. 8.—Part of one of the scattered ovaries in a specimen in which ova are 
passing into the uterus. The outlines of the cells can be distinguished in nearly all 
cases. 
Fie. 9.—Two yelk masses from the same specimen as Fig. 8. Hach contains 
nucleated cells and yellowish globular bodies, corresponding exactly to those found in 
the commencement of the uterus (cf. Fig. 2). a. nucleated cells, which will form 
food yelk ; x. yellow-coloured material, which will probably give rise to the cell. 
Fig. 10.—Three yelk masses, from a specimen in which the uterus is filled with 
embroyos which have undergone a considerable amount of development. Hach 
forms a mass in which large nuclei are present, but only a comparatively indistinct 
separation into distinct cells, and no trace of the yellowish shell material. 
