THE SEPARATION OF THE GERM-LAYERS, ETC. 



283 



organ. The posterior rudiment is specially large. The two branches, which 

 diverge at a wide angle, carry diverticula and thus form the lobed masses of 

 the lower pair of salivary glands (GRENACHEB, No. 14 ; JOUBIN, No. 22). The 

 unpaired part of the rudiment, which corresponds to the common section of 



KK;. 1:53. -Sagittal section through an older embryo of Luligo vulgaris, somewhat 

 diagrammatic (original), it, anus; a.ds, external yolk-sac; ar, arm-rudiment; bs, 

 caecum of tin- stomach; c-g, cerebral ganglion; d, yolk; de, yolk-epithelium; ect, 

 ectoderm;/, tin; h, lu-art; /.r/.s, internal yolk-sac ; m, mouth; Hid, intestine; mes, 

 incscxlenu ; itit/, stomach; nit. edge of mantle; ot, otocyst ; pg, pedal ganglion; /, 

 radular sac; ad, shell-sac; */>, salivary gland; fb, ink-sac; tr, funnel; rd, stomo- 

 ; rif. visceral ganglion. 



the efferent duct, greatly lengthens, for, in the adult, the lower salivary glands 

 lie far back. The rudiment of the radular sac also undergoes modification, 

 the part of its wall which is turned backward and inward thickening and the 

 radula being secreted in the way described above (p. 201 and Fig. 91 A). 



