330 MEMOIIJS OP THE NATIO^^AL ACADEMY OF SCIENCES. 



Pl. VIII. Figs. 1-4. Horizontal sections of the same. Fig. 1. Section passing through the base of the cerebral 

 ganglia and involving the lower tegumental nerves, or nerves to the sensorial jiapilla .situated in 

 front of the first pair of appendages (probably the "neuropore" of I'atten). Figs. 2, 3, and 4, 

 sections passing through the lower branches of the mushroom bodies. Figs. 5, 6, 7, sagittal sec- 

 tions of brain of a small Limulus of the same size as above indicated. Fig. 5, represents a sec- 

 tion through the brain passing through the lateral-eye lobe and nerve; also involving the ganglia 

 of the first and of the second pair of .appendages, forming the anterior portion of thecesophage;:! 

 ring. Fig. 6. Section passing through the median-eye lobe and nerve; also the cerebral lobe ami 

 the nerve to the first pair of appendages. 



Pl. IX. Figs. 1-7. Sagittal sections through the brain of an adult Limulus, beginning near one side. In this and 

 plates X to XVI the pink portions represent the cortical masses of small ganglion cells of the 

 mushroom body. 



Pl. X. Figs. 8-13. The same series coutinued to the middle of the brain, representing, as before, a selection of the 

 typical sections. 



Pl. XI. Figs. 1-5, and 7. Transverse (frontal) sections of the brain of an adult Limulus from before backwards. 



Pl. XII. Figs. 6, 6a, 8, 9. The same series continued backwards. Fig. 6a. Enlarged view of the left median-eye 

 lobe. Fig. 8. Enlarged view of the median-eye lobes a little further back. The fibers arising 

 from the large ganglion cells pass inward towards the median line of the brain. 



Pl. XIII. Figs. 10-15. The same series continued backwards. 



Pl. XIV. Figs. 16, 17. The same series continued. Fig. 18. Transverse section through the brain of a young Limu- 

 lus, passing through the cerebral lobe, and its commissure; externally is the bulb of the cerebral 

 lobe (6. c. I.). From this portion of the cerebral lobes arise the stalk of the mushroom body on 

 each side, sending otf descending, lateral and ascending {asc. st. m. 6.) branches. 



Pl. XV. Figs. 19, 20. Transverse sections of the same lower down, and involving the oesophagus. 



Pl. XVI. Figs. 1-12. Transverse sections through brain of a young Limulus. and passing back through the oesopha- 

 geal ring to the basal portion of the veutral cord. Fig. 6 (section 196), pr. a. com., pre-cesopha- 

 geal commissure, connecting the ganglia of the first pair of appendages. It will be seen that in 

 Limuli about two inches in length exclusive of the caudal spine this commissure is quite free from 

 the posterior part of the brain. Compare also Pl. xxxiil. This is apparently the "Commissure 

 deutocerebrale" of Viallanes. See Fig. xix, p. 312, copied from his work. Figs. 8 to 12 should 

 be turned around, as these sections pass behind tlie cesophagus. Fig.8, post. oc. com., represents the 

 second commissure, ». e., the first one behind the ci'sophagus. Figs. 9 to 12 pass through the begin- 

 ning of the ventral cord. 



Pl. XVII. Figs. 1-6, All representing the embryo of a single stage showing the ganglia of the median eyes of the 

 lateral eyes, and the central ganglia. I., labrum. The pit directly in front of the labrum may 

 possibly be the ' ■ neuropore " of Patten ; n' to n', the neuromeres, or embryonic ganglia ; /., the two 

 pairs of sense or glandular organs visible at this stage ; lat. h., the "lateral heap" or dorsal organ. 



Pl. XVIII. Figs. 1-5. Sections through the larva of Limulus, showing the brain and nerve ganglia. Figs. 6-9. The 

 same of the trilobite stage. 



(Compare also the figure of a better section of the larva as a whole in my memoirs published 

 in 1880 in Anniv. Memoirs of Boston Society of Natural History, Pl. in, Fig. 2.) 



Pl. xix. Figs. 1-9. Sections through the larva of Limulus. 



■^L. XX. Figs. 1-6. Sections of the lower part of the body, showing the nervous system and abdominal legs of the 

 trilobite stage. Figs. 6 and 6a, 66, 6c, sections of the abdominal legs and gill-plates of the early 

 larvje. Fig. 6, section of the first abdominal leg (operculum), and of the second, bearing five gill- 

 leaves, and the rudinieut of a sixth. Fig. 6a. The same enlarged. Fig. 6ft and 6c, other sections 

 of the same from the same larva. 

 All the figures on Plates i to xx have been drawn with the camera by the author. 



Pl. XXI. From a microphotograph of the section of the brain represented by Pl. i, Fig. 3. 



Pl. XXII. From a microphotograph of the section of the brain a little below. 



Pl. XXIII. From a microphotograph of the section of the brain represented by PI. I, Fig. 6, where the parts are let- 

 tered. 



Pl. XXIV. From a microphotograph of the next section below. 



Pl. XXV. From a microphotograph of the section represented by Pl. ii. Fig 8. 



Pl. XXVI. From a microphotograph of the section represented by Pl. ii. Fig. 10. 



Pl. XXVII. From a microphotograph of a section still lower down. 



Pl. XXVIII. From a microphotograph of the second section below Pl. xxvii. 



Pl. XXIX. From a microphotograph of the section represented by Pl. in. Fig. 12. 



Pl. XXX. From a microphotograph of the third section below that represented by Pl. iii. Fig. 14. 



PI. XXXI. From a photograph of a drawing, by the author, of a section much lower down than that represented by 

 Pl. V, Fig. 22. 



Pl. XXXII. From a microphotograph of a transverse horizontal section through the brain of a young Limulus, pass- 

 ing through the lower part of the cerebral lobes, with the commissure uniting them and the 

 (Esophagus behind. Osmic acid preparation. (Section 136. ) (The same section is represented 

 on PI. XIV, Fig, 18. 



