ME.MOlliS Ol- TIIK NATIONAL ACADK.MV OF SCIKM KS. 



293 



pnivcd by PcIsoikht to <-oiitiiii (lie aiitcimiil {jimKlii't tliiuiffli tlic nerves branch off at a coiisid- 

 erablo distance fn>in the brain, on the side of the tes(>i»ha;;u8. A sU?\) higher is seen in the brain 

 of iso]K>ds, where, as we have described and li},'un'<l • the tirst and second antennal ganglia of 

 Asellns are not closely coah'sced and consolidated with the optic and cerebral lobes, but are sepa- 

 rate from the brain and situated below ami jiosterior to it, tii(iu;fh in front of tlio (esophagus. The 

 most complex type of crustacean brain is that of the higidy specialized l)c<ap«da. 



Tlie brain of adult insects is on the same liigh plane as that of decapod Crustacea, the optic 

 and antennal lobes being invariably (X)aleseed with the cerebral, the whole mass being separated 

 from the infra usoi)liagcal ganglion, and so it is with the brain of myrioixxls. 



The Arachnidaii lirain is very distinct in its external appearance Irom (hat of insects or 

 Crustacea. 



Prof. Pattcnt has given us what is ai)parently a clear and accurate figure on an enlarged 

 scale of the scori)ion's central nervous system, which we take the liberty to copy, with a 

 change in position and consetiuent change in the lettering. 



TOO.! 



l<rt.c.iv i 



s.lYs'trtocW 



Fio. IV.— Brain of adult scorpion, conntrncted by mcona uf suctions and dissections. A. B., accessory brain; H. B.,biud brain: M. B., mid 

 brain ; F. B., fore brain : a. eo.. anterior rumnii.ssurcs; a. A. n. w, anterior haemal nerves of the tburacic ueuronienm; c. sy. cranial syiupa- 

 tbitic ( I) ; (;', large gangliun derived from the seginont;il and co.\al sense organs, and giving off many brancbes to tbu scattered sense organs 

 in skin of obel» ; g. /., ganglion fusiforme ; g. noil., ganglion nodosiiui or g. striatum ; h.n. «., a very delicate root, probably representing the 

 faumal nerve of the third fore-brain neiiromere, partially fused with the bffimal nerve of the cbeliceral segment; h. v.' and A. v.", the inde- 

 pendent anterior and posterior nerves of the tint vagus neuroniore : h. nMmil h. v.'', the four partially fused bienial nerves of the second and 

 third vagus neoromerea; lal. e. n., lateral-eye nerve : m, mouth: tnr. n., median-eye nerve; m. »t. ii.. median atvmodieal rostral nerve; n. t., 

 comb or pectinal nerve; ng.\*, neural ganglia at the base of the neural nerves; n. n.i-6, neural nerves of the thoracic segments; A. t>.l-«, 

 roots of the neoral vagus nerves: pA. n.'-*, posterior hienial nerves of thetbnrax: p. Co., posterior brain commissure; f. J. (str. body), semi- 

 lunar lobe or first brain segment: r. m., retractor musctos to (esophagus. — After Patten. 



Prof. Patten incorrectly applies the term "brain" to tlie entire central nervous system, only 

 excepting the abdominal ganglia, dividing the brain and (esophageal ring or mass into three divis- 

 ions, viz, the fore, mid, and hind brain, as indicated in his ligure. But restricting the term brain to 

 the .supra (esophageal ganglionic mas.s, it will be seen that tlie ganglia which innervate the tirst 

 l)air of appendages, though separate in the embryo, are in the adult -scorpion clo.sely united with 

 the' brain, thoiigli there is a .slight con.striction between tlie two portions of the brain, viz, between 

 the '-mid brain" (or rostro-maiidibular ganglion of St. Kemy) and the -'fore brain." 



It is desirable also, for the sake of clearness, not to consider the "hind brain" as a part of 

 tlie brain, since it is a i)ost-a'sopliageal mass, innervating the cephalic and thoracic appendages, 



•structure of the bruiii of Hcttsili'-eyrd Crustacea, 

 t Quart. Joum. Micr. Sc, 317, 1890. 



