MEMOllJS OF THE KATIONAL ACADEMY OF SCIENCES. 



291 



is sc'imrated from tlie (i'so|ilm;,'i'al liii;? by a slight but yctdistinet coiistrictioii seen both above and 



bt'iieath, the i stiiolion on the n|i|icror dorsal side passing Jnsl behind the hiterai eye h)bes, viz., 



those sending lu-ives to the huge hiteral conijiound eyes. It is Inoatler at the base tlian it is tiiiek, 

 and narrow m front, seen from above, so tliat it is about a fourth narrower in front (in front of 

 the origin of I lie lateral eye nerves) than at the base or posterior end. 



The viiiitral or under sitle is quite reguhirly convex and fuller and rounder than above; tlie 

 eonvexity or fullness is greater in the center and chops or extends down considerably below the 

 origin of the nerves of the lirst pair of appendages, this being the poition below the central lobes 

 and which is lillcd with the rulllelike masses of small, ganglionic or chromatic cells. 



The brain of a Linnilus al>out lt» inches h>ng, exclusive of the caudal spine, is about mm. 

 in diainitcr: it is conico sphcroiiial, l>roail and llattencd from above, and on the under side full 



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MA, If 



Fia. I. Brain and a-wphageal riiij; of Limulus, seen from above; dr., 

 brain: cc, cotumisHunrfl behind tho w8opha|;uii; m. eye n.. lueilian-uyo 

 ntrvf: lat.ti/e «., laiiTiilejo uurvo: i-vi, ncrvca lo tho sin pairs of cc|ilia- 

 lothoracic appendages or leg»; p. c Tcntral cord; 2. Crr;., lower tegumental 

 ne^^'C ; Ug.n., other tegomental nerreti. 



Fio. n.- -Ventral view of tho brain and n'sopbageal ring 

 of Limnlns. in. /r. t<!<;.,ni<'<liofront;il tegumental nerve; 

 6. ttg.n.. lower tegumental ner\e or nerve to the senitorial 

 pit. Author del. 



and roundetl; on the upi)cr side is a broad, shallow, median furrow, indicating that it is double. 

 In the young Limulus, with a body about 2 inches long, exclusive of the caudal spine, the brain 

 is longer, narrower, and less spherical. 



Three pairs of nerves and a median unpaired one (the occllar) arise from the upper third of 

 the anterior face of the brain. The two lateral-eye nerves are the largest, arising very near the 

 upper side of the brain, one on ea<;h side of the median furrow, so that the second and third sec- 

 tions made by the microtome pass through them. Next below (from above downwards) is the 

 origin of the single nerve sent to the two ocelli. We have not traced this nerve as fai- as the 

 ocelli, but Milne Kdwards states that neai the ocelli it divides into two branches. On each side 



