312 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Another organ which is characteristic' of tlie scorpion's brain we have failed to detect in that 

 of Limuliis, nor does YiaUaiies mention it. Saint Eemy thus describes that of the scorpion : 



The structure which, for want of a better name, we shall designate under the name of wallet-shaped organ 

 (orijane en bissac) to recall its general form, occupies the internal and middle part of the cerebral lobe. It comprises 

 two segments united by a much smaller middle portion in the form of a neck (p. 224). 



Still another organ also present in the scorpion's brain which we have not found in the brain 

 of Liniulus, and which is not mentioned by Viallanes, is the olivary body. It is situated in the 

 ])osterior region of the cerebral lobe below the wallet-like organ near the median line; it is an 

 olive-shaped mass of dense punctured substance and situated obliquely. 



Considering, then, the fact that the deutocerebrum or its homologue is in Limulus separate 

 from, where in Arachnida it is fused with the brain ; also the differences in the shape of the cerebral 

 lobes, the immense development of the ruflfle-like plates or masses of small chromatic ganglion 

 cells forming the pedunculated or mushroom bodies; the small number of large ganglion cells; 

 the absence of the wallet-shaped and of the olivary organs found in the brain of scorpions, and 



ad 



1 \ 1 1 t / / 11 1 s Irfm T iiuxltl 111 rchet ( f tilt brain of Limulus, madeof ■wax, seen from 



tl I II literal o-\ e lobe meJ mctlian cyo lobe-, m. c.n., median-eye nerve; »i.n., 



II I I 1 IHues) mb m b m b mb lobules of the mushroom or pedunculated body ; 



c f II 1 J I I 11 I I 1 il niufahroom bodj c I cerebral lobes; r.t.n. and r n. (..recurrent tegumental 



ULivi n a p ULrM3(l hi t piircf mtiilt^i (clu-la i il ntive of Tiallanea) c com cerebral coinniiasure; d.c. com., deutocerebral com- 

 missure del deutoterebril lobes v n root of visceral or sympathetic neivous 8\stem — After Viallanes. 



It IS to be obsei vtd that the median eye g.inglia are not < orrectly represented by the model, the horseshoe shaped mass simply repre- 

 fionting the fibres. See my PI. vn. Pig. 1. This empty median oval space is, in nature, filled -with large and small ganglia cells, and the 

 roots of tile fibres originating from them. 



the absence of the peculiar medulhiry plates present in the optic loljes of spiders, we see that 

 wliile the brain of Limulus is in most respects simpler, it also presents noteworthy differences from 

 that of the Arachnida.* 



* Since this paper was put in type, ;iud ;i, few days before obtaining the proof, I received the Annales dcs 

 Sciences Naturelles, Zoologie, Nos. 4, 5, 6 for March 10, 1893, containing M. A'iall.incs' liiial paper <ni the brain 

 of Limulus. 



The account of the internal structure of the brain is brief, occupying but five pages, and ends with an " Jjierfu 

 ijvndral de V organisation dii si/sicme nerveux dcs ArticuUs." The article is illustrated with two folding plates. Only 

 two actual sections of the brain of Limulus are represented. One-(Pl. 10, Fig. 17) represents a horizontal section 

 pa.ssing through the lateral-eye g;ingIion (" ganglion optique") of one side, ;uiil the other ( Fig. l.S) of a horizontal 

 section lower down passing through the stalk of the pedunculated body. 



This last figure clearly shows what my sections has failed to do, except p:irtially, the well-ilelined stalk of the 

 mushroom, or iiedunculated body, and shows that what iu the first place I h;id described as the "nncleogenous 

 liodies," are lobules or branchiis of a pair of organs probably homologous with those of insects. This leads me to 

 accept M. Viallanes' view of the homology of these extraordinarily developed organs with the two mushroom bodies 

 of insects. In ai eordaiKc with this view I have corrected the text of tlie present article. Viallanes has also pointed 

 out and drawn the chiasmii of the median eye, structures which I had failed to see: and ho shows that the the basal 



