308 PROCEEDINGS OF THE ACADEMY OF [1887. 



(ee) ectoderm. 



{eti) entoderm. 



{Hvi) heart muscle. 



(igc) inner glandular cushion. 



(m) inner mantle, 



(ini) intestine. 



(VHy) I'hypophyse. 



(m. h.) muscular bands. *"' 



(m/) muscles fibres. 



(mgc) middle glandular cushion. 



(inib) middle intermediary band. 



(nf) nerve fibre. 



{ng) nerve ganglion. 



(oe) oesophagus. 



(ogc) outer glandular cushion. 



(oib) outer intermediary band. 



(pc) pigment cells. 



(ph) pharynx. , 



(vo) visual organ. 



Explanation of Figures, PL XIII. 



Fig. 1. Section of inner and outer mantles. 



" 2. Surface view of ectoderm, 



" 3. Portions of three muscle fibres from muscular bundle. 



" 4. Section through one of the muscular bundles of the trunk 

 showing its position in the inner mantle, 



" 5. Seven muscle fibres as seen from a surface view of one of 

 the bundles. 



" 6. Transverse section of the entire gill. 



" 7. Longitudinal section through a portion of the gill, on the 

 plane of cb. in fig. 6. 



" 8. Showing one half of a transverse section of the endostyle 



" 9. Longitudinal section through the oesophagus. 



" 10. Transverse section of the intestine and the two coecal ap- 

 pendages. 



" 11. View of tlie outer surface of a coecal appendage. 



" 12. Striated muscular "fibre cells" composing the wall of the 

 heart. 



" 13. Vertical section through brain, visual organ, and I'hy- 

 pophyse,. 



