30 



THE NAUTILUS. 



Figure 6. Diagrammatic 

 opening of genital ducts. 

 G 0 — Genital opening 

 N C — Nerve cord 

 CI Ch — Cloacal chamber 

 I G — Inner gill 

 0 G —Outer gill 

 Ft —Foot 



i section of Calyculina to show 



P — Pericardium 



K — Kidney 



R — Rectum 



Blv — Posterior aorta 



M —Mantle 



Figure 7. Frontal section of neutral part of inner gill, show- 

 ing fusion of the two lamellae. Calyculina. 

 I L — Inner lamella Ifj — Interfilamentary junc- 



0 L — Outer lamella tions 

 Bis — Blood space Ct — Cross threads 



Figure 9, Part of inner wall of the brood pouch of Cyclas. 

 (Copied from PoyarkofT). 



L — Leucocyte lodged at base of cells 

 F — Leucocyte just entering wall of pouch 

 A — Leucocyte beginning to divide 

 N — Polynucleate cell 



Plate VI. Figure 10. Shell of Spaerium simile showing 

 growth lines. 



U — Umbo i, 2, 3, 4, — Growth lines 



Figure 11. Diagrammatic reconstruction of a portion of the 

 inner gill of Calyculina, showing the relation of brood pouches 

 to gill filaments. 



/ L — Inner lamella Em — Embryo 



0 L — Outer lamella 1 W — Inner wall of brood 



CI Ch — Cloacal chamber pouch 



If J — Interfilamentary junc- 0 W — Outer wall of brood 



tion pouch 

 G F —Gill filament Bis —Blood space 



