MORPHOLOGY OF BRAIN AND SENSE ORGANS OF LIMULUS, 95 



In Fig. 51 it passes through the middle commissure, the peduncles of the 

 cerebral hemispheres, and the last connection of the hemispheres with 

 the ectoderm, x 275. 

 Fig. 52. — Cross-sections of the brain of an adult Limulus, passing through 

 the slender peduncles on which the enormous cerebral hemispheres are sup- 

 ported. The plane of section cuts the anterior border of the middle commis- 

 sure. Its position is shown on a younger brain by the line 21, Fig. 43. 

 X 15. 



EXPLANATION OF PLATE 5. 

 Reference Letters to Plate 5. 



a. p. st. Anterior pons stomodsei. at. n. Nerve to antennae, at. neu. 

 Antennary neuromere. a. st. g. Anterior stomodseal ganglion, a. st. n. 

 Anterior stomodseal nerve, br. 1 — 3. Brain lobes, c. Brain commissure. 

 c. e. Convex eye. ch.g. Ganglion to cheliceral nerves, c.l. Cerebral lobes. 

 ch. n. Cheliceral nerve, ec. p. e. Ectoparietal eye. en. p. e. Endoparietal 

 eye. ep. Epiphysis. F. B. Fore-brain, g. hab. Transverse tube of nervous 

 substance, g.v.l — 3. Invagination of optic ganglia, i. md. Inner mandible. 

 i. md. n. Inner mandibular nerve. I. Labrum. /. e. n. Lateral eye-nerve. 

 I. st. g. Lateral stomodaeal ganglion. I. sy. Lateral sympathetic nerve. M. B. 

 Mid-brain ^ antennal or cheliceral neuromere. m, sy. Median sympa- 

 thetic nerve, n. ec. p. e. Nerve to ectoparietal eye. n.en.p.e. Nerve to 

 endoparietal eye. n, I. Labral nerve, n. oc. Nerve to ocelli, n. r. p. e. 

 Nerve-roots to parietal eye. o. To. Nerve of Tomosvary. oc. Ocelli, o. e. 

 (Esophagus. 0. g. 1 — 3. Optic ganglia, o. md. n. Outer mandibular nerve. 

 0. md. Outer mandible, p. e. Parietal eye. p. g. Pedal ganglion, p. m. 

 Primitive mouth, p. n. Pedal nerve, p.p.st. Posterior pons stomodsei. 

 s. I. Semicircular lobes, v. c. Ventral cords. 



Fig. 53. — Diagram of nervous system of an insect, showing relations of 

 stomodseal and trunk sympathetics to the cephalic lobes and ventral cords. 



Fig. 54;. — The same, with the stomodseum evaginated, to illustrate what 

 was probably the original distribution of the stomodseal nerves. 



Fig. 55. — Hypothetical embryo seen from the side, showing distribu- 

 tion of stomodaeal nerves. 



Fig. 56. — The same, with the stomodseum evaginated. 



Fig. 57. — Diagram of the cephalic lobes and stomodseal nerves of an insect 

 embryo (Holometabolic). 



Fig. 58. — Same of a scorpion. 



Fig. 59. — Same of Limulus. 



Fig. 60.— Brain of Acilius at beginning of pupal stage, slightly diagram- 

 matic. 



