94 WILLIAM PATTEN. 



Figs. 35 — 40. — A series of longitudinal sections tlirough the brain in 

 about the stage sliown in Fig. 24. There were 28 sections in the series, sec- 

 tion 14, Fig. 25, passing through the sagittal plane. The position of the 

 sections is shown on Fig. 24 by the numbers 35 — 40. Only those sections are 

 represented that show some variation in the invaginations. 



Fig. 41. — Diagrammatic longitudinal section through an early stage of the 

 brain of Limulus to show the relation of the median eye-tube to the anterior 

 wall of the brain. 



Fig. 42. — Same of the scorpion. 



Fig. 43. — Right half of the brain of a young Limulus about 3 inches long, 

 viewed from its cut surface. The outlines and proportions of all the parts 

 are drawn from a wax plate model, same as that in Fig. 49, and is diagram- 

 matic only in so far as the invagination cavities of the infundibulum, optic 

 ganglion, median eye, and olfactory organ and neuropore are represented as 

 persisting up to this period instead of disappearing soon after their formation. 



Fig. 44. — Cross-section through the dactylopodite of a Limulus about 8 

 inches long, showing general distribution of the cuticular canals for the gusta- 

 tory and temperature organs. The gustatory canals are most abundant along 

 the anterior cutting edge of the joint. The cuticula about the canals is in 

 some places stained black by the osmic acid used for that purpose. 



Fig. 45. — Under surface of a young Limulus 61 mm. long, showing the 

 position of the olfactory organs in reference to the mouth, also its radiating 

 choroid plexus of white pigment-cells, x 2. 



EXPLANATION OF PLATE 4. 



Fig. 46. — Nervous system of Limulus in its second larval stage seen from 

 the dorsal or haemal surface, x 66. 



Fig. 47. — Cephalo-thoracic nervous system of the same seen from the 

 ventral or neural surface. X 66. 



Fig. 48. — Nervous system of Limulus about 2^ inches long, seen from the 

 neural surface. Constructed from sections and dissections. The sympathetic 

 system is not represented in Figs 36 — 38. x 15. 



Fig. 49. — Fore-brain region of a young Limulus about 3 inches long, seen 

 from the haemal surface. The drawing is made from a wax plate model, 

 enlarged about 100 diameters. The drawing is reduced to about 30 

 diameters. 



Figs. 50 and 51. — Cross-sections of the brain of Limulus in the second 

 larval stage (see Figs. 46 and 47). 



In Fig. 50 the section plane lies some distance back of the peduncles, and 

 shows the overlapping of the cerebral hemispheres. 



