Plate I. 



Fig. 1. — Blood corpuscles taken from a living specimen of the adult Lingula. 



x 310. 

 Fig. 2. — Blood corpuscle treated with acidulated methyl green, x 800. 

 Fig. 3 a, b. — Two leucocytes taken from a living specimen, x 380. 

 Fig. 4. — Star-shaped leucocyte, from a hsematoxylin-erythrosin preparation. 



Blood corpuscle is also drawn for comparison of size, x 729 (immers). 

 Fig. 5. — Transverse section through the epithelial ridge. x 729 (immers). 

 Fig. 6. — Leucocyte embracing a spindle body ; a compact body by it. 



x 729 (immers). 

 Fig. la. — Spindle body with two bundles, x 380. 



b. — Spindle body with three bundles, x 800. 



c. — Spindle body with a constriction, x 380. 



d. — Spindle body with a bundle bent within the membrane. x 380. 



e. — Fragment of spindle body. x 380. 



f. — Spindle body with fibres running in various directions, x 380. 



g. — Spindle body in the dendritic organ with very loose fibres in the 

 cell membrane, x 729. 

 Fig. 8 a.— | 



b. — [Three spindle bodies treated with acidulated methyl green. 



c— J x 490. 



Fig. 9. — Transverse section through the mantle perpendicular to the palliai 



sinus. Here two epithelial ridges are seen as the section passes the 



point of bifurcation of the palliai sinus, x 80. 

 Fig. 10. — Transverse section through the mantle perpendicular to the epi- 

 thelial ridge. Hrematoxylin-orange G-erythrosin preparation, x 490. 

 Fig. 11. — Portion of a section of the mantle, x 420. 

 Fig. 12. — Dendritic organs (d. o.) on the ventral body wall exposed. Sub- 

 limate preparation, x 2. 

 Fig. 13. — Transverse section through a dendritic organ of the adult. x 500. 

 Fig. 14. — Transverse section through the young Lingida of 5.5 mm. shell 



length, showing only the dendritic organ, x 729 (immers). 

 Fig. 15. — Blood corpuscle in a stage of transformation into the compact 



body. The nucleus is pushed aside and the cytoplasm becomes 



granular, x 729 (immers). 

 Fig. 16. — Transverse section through the epithelial ridge of the adult. A 



compact body is imbedded in the epithelium. Three blood corpuscles 



are shown for comparison, x 729 (immers). 

 Fig. 17. — Two compact bodies of different sizes ; both are much smaller 



than usual compact bodies. The splitting can here be seen, x 729 



(immers). 

 Fig. 18. — Compact body from the dendritic organ, half of which has been 



metamorphosed into fibres, x 729 (immers). 

 Fig. 19. — Spindle body with the remnant of a compact body from a section 



through the dendritic organ, x 729 (immers). 



