MEMOIKS OF THE NATIONAL ACADEMY OF SCIENCES. 



311 



upper iiiul lower jwrtion, but without iiuy stalk piissiiig- downward into the central portion of the 

 brain. 



Dr. Saint llemy describes this body at length under the name organe xtratijie posterieur, 

 aud says that it is situated on the very salient posterior and upper border of the brain, forming a 

 prominent projection above the punctuated mass of the cerebral lobes. It comjirises a principal 

 medullary jjortion and a cellular covering. It is formed of parallel alternate clear and obscure 

 bands. 



That this organ is apparently not homologous with the mushroom bodies of insects appc^ars 

 to be provetl by the fact that it is single, not a x^aired organ. 



ant gi irv 

 HI "w orsr 



cer.pvau 



ami) 



cer. §"ang- 



!r;i tifiedLody 



amb 



Fig. XIV. — A, horizontal section passing through the upper part of the brain of the scorpion (Buthv^occitamteAmovs.) through the lower 

 optic lobe or ganglion, cer. gang., cerebral ganglion; I. eye n., lower eye nerve: amb, anterior medullary bell of the lower optic giingUon; 

 m. b., middle medullary hall of the same ; ped., common peduncle of the optic lobules ; parts of the stratitied org.an or body ; I. sir., lower segment ; 

 u. xtr., upper segment ; apatr, anterior plate (lame) of the upper segment of the same ; a. gang, m ., anterior ganglion-mass : an. i. I., antero- 

 intemal lobule; w. or^, principal medullary mass of the anterior segment of the wallet-shaped organ ; v, vessel (artery) ; B, longitudinal 

 (sagittal) section of the same passing through the union of the internal third with the midtUe third of the brain. Very young individual, 

 X 53 diams., g. w. b., principal glomerulated mass of the posterior segment of the wallet-shaped organ ; principal medullary mass of the an- 

 terior segment of the wallet-shaped organ ; ant. g. m., anterior ganglion mass ; chcl. lobe, ganglion innervating the first pair of appendages ; 

 e.f., commissural fascia — After Saint Remy. 



In the scorpion (Fig. xiv, str. body) the stratified body differs somewhat from that of sjiiders, 

 but is essentially the same. "But the most interesting feature about it," says Saint Eemy, "is 

 the relation which exists between this organ and the optic lobe by the medium of the common 

 peduncle." Although the stratified body of Arachuida is described aud figured as unpaired, yet 

 in deference to the opinion of Saint Eemy I provisionally accept his view that it is the homologue 

 of the pair of pedunculated bodies of insects. I may aild that it is a matter of sui'prise to me that 

 M. Viallanes does not dwell more on the remarkable differences between the brains of Limulus aud 

 of the Arachuida, particularly the great differences between the mushroom-bodies of Limulus and 

 their homologues in Arachuida, since he adopts the opinion that Limulus is an Arachnidan. On the 

 other hand these striking differences in the morphology of the brain tends to my mind to furnish 

 additional proof that Limulus is the representative of a different class of Arthropods. 



