MOEPHOLOGY OF BEAIN AND SENSE ORGANS OF LIMULUS. 89 



repeat these objections to give them serious consideration^ but 

 only to emphasize the fact that the solution of the Vertebrate 

 problem is not merely the filling in of a gap in our system of 

 classification, but this solution will necessitate the recon- 

 struction of a vast deal of that preconceived morphological 

 philosophy which at present forms the most serious obstacle 

 to the perception of the genetic relation between Vertebrates 

 and Arachnids. 



Grand Forks, N. D. ; Nov. 29th, 1892. 



EXPLANATION OF PLATES 1 to 5. 



Illustrating Mr. William Patten's paper " On the Morpho- 

 logy and Physiology of the Brain and Sense Organs 

 of Limulus." 



EXPLANATION OF PLATES 1 and 2. 



Reference Letters to Plates. 



ax. n. Axial nerve, bl. v. Blood-vessels, c. c. Cuticular canal, ch. t. 

 Cbitinous tubule, ch.t'. Proximal end of chitinous tubule, g. c. Ganglion- 

 cells, g. 0. Gustatory organs, g. p. n. Ganglion to the pedal nerve, gs. c. 

 Gustatory cells, g. and t. or. Gustatory and temperature organs, i. md. 

 Inner mandible. I. ol. n. Lateral olfactory nerve, m. Muscle, md. n. Man- 

 dibular nerve, m. i. m. Flexor muscles to inner mandibles, m. ol. n. Median 

 olfactory nerve, n. Nerve, n. c. Slender nerve-like cells surrounding the 

 base of the chitinous tubule, n. co. Nerve collar, n. and n'. Primary and 

 secondary nuclei of the gustatory cells, n.fbl. Cone of nerve-fibrillae inside 

 the spindle, o. md. Outer mandible, p. g. Yellowish-brown pigment 

 granules, p. n. Pedal nerve, s. c. c. Swelling in cuticular canal, s. ch. t. 

 Swelling on chitinous tubule, sp. Spindle on gustatory cells, sp.f. Spiral 

 fibre, s. sp. Canal containing pigment and fibrous cells leading to spines. 

 t. 0. Temperature organs, v. Deeply stained varicosities on the nerve- 

 fibrillse within the spindle, w. p. White pigment-cells. 



