184 BRACE. 



EXPLANATION OF PLATE XXL 



Fig. I. Frontal view of the central nervous system, reconstructed from sec- 

 tions, (x 210.) 



Fig. 2. Ventral view of the brain, (x 1200.) 



Fig. 3. Dorsal view of the brain, showing its bilobed form, (x 1200.) 



Fig. 4. Frontal section near the middle of the brain, showing the first pair of 

 nerves. ( X 800.) 



Fig. 5. Frontal section next above Fig. 4. ( x 800.) 



Fig. 6. Sagittal section of the brain in the plane of the anterior nerve and the 

 posterior lobe. ( x 800.) 



Fig. 7. Sagittal section of the brain a little nearer the middle than Fig. 6. 

 ( X 800.) 



Fig. 8. Sagittal section near the middle of the brain, showing a single layer of 

 cells on the dorsal side. ( x 800.) 



Fig. 9. Oblique section of the brain, showing the posterior lobe and the roots 

 of the first and second cephalic nerves. ( x 800.) 



Fig. id. Cross-section of the brain in the plane of the commissure. { x 800.) 



Fig. ii. Frontal section through a segment of the ventral nerve cord, showing 

 the roots of the lateral nerves and of the connecting commissures, (x 1200.) 



Fig. 12. Cross-section of the ventral nerve cord in the thoracic region, show- 

 ing the ganglia connected by a commissure. ( X 800.) 



Fig. 13. Drawing showing the mouth with the furrows leading to it, and the 

 prostomium, ciliated on the ventral side, (x 1200.) 



Fig. 14. Pear-shaped sensory cell, with vesicle containing a refractive body. 

 (x 1200.) 



Fig. 15. Sense organs composed of several cells similar to those of Fig. 14. 

 (X 1200.) 



Fig. 16. Partial diagram showing the position of the compound sense organs 

 on the ventral surface of the prostomium. ( X 1 200.) 



