Memoies of the national academy of sciences. 305 



As we have already stated M. Viallanes' classification of the regions of the Crustacean and 

 insect brain into three regions, viz, jivoto, deuto, and tritocerebnim, does not apply to that of Limulus. 

 Ill my xiremiminary paper I pointed out that no deutocerebrum or tritocerebriiiii is reineseiited in 

 the brain of Limulus, and it is to be observed that Viallanes regards the brain as com^iosed of two 

 ])airs of ganglia, the first being the protocerebrum, while as to the second he is doubtful, and pro- 

 visionally calls it the " cerveau postcrieur." Viallanes " protocerebrum" is what we regard as the 

 brain proper, and consists originally-of three pairs of neuromeres, becoming respectively the ocellav 

 or median-eye ganglia, the lateral-eye ganglia, and the cerebral ganglia. * 



What Viallanes regards as the posterior brain, and as to the homologies of which he expresses 

 himself as in doubt, we regard as a part of the oesophageal ring, and as postcerebral. This pos- 

 terior brain gives rise to the cheliceral nerves. The " Commissure transverse pre-oesophagienue " 

 I have detected since Viallanes has called attention to it. 



Throwing out then, Viallanes cerveau posterietir,* as not forming a part of the genuine brain of 

 Limulus, we will return to the braiu proper, or prestomial mass, viz, the protocerebrum of Viallanes. 



IX. — THE HOMOLOGIES OP THE ^O-OALLED " NUCLEOGENOUg " OU "PEDUNCULATED BODIES." 



M. Viallanes diiScribes at some length the structure of the series of plates which We originallyt 

 'called coliecliVely the " nucleogenous bodies, " and the nature and homologies of which seemed to 

 Us pi\*Mematical. He remarks : -'To each of the protocerebral lobes is annexed an organ which, by 

 k:'ei3i8on of its anatomical relations and its histological structure, should be assimilated to the 

 pedunculated body of insects. The pedunculated body of Limulus has an arborescent form. The 

 lower extremity of its stalk penetrates into the corresponding protocerebral lobe, its upper 

 extremity is divided dtchotouioufily Into a great number of braUches. These last, which end in 

 truncated eslremltie;*) ilre entirely covered by a thick cortex of small cells very deficient in proto- 

 plasm, very deeply colored by stains, emitting very fine fibrilhe, in a word rigorously similar to 

 the elements which form the cellular vestiture of the pedunculated body of insects." 



The pedunculated body attains in the Limulus an extraordinary development greater than any other Arthroiiod 

 known, because it by itself alouo forms certainly at least ,^(Sf of the total mass of the braiu. This fact is all the 

 more remarkable since up to the j)resent time and not without important reason it haa been agreed to consider the 

 development of the pedunculated body as correlated to that of the mental faculties (pp. 2-3). 



Fur years the true relations of these masses or plates which I have called the " nucleogenous 

 oOdies" liave beeu a gl'eat puzzle to me; they are so numerous and form so large a proportion of 

 the brain; bitt after an examination of the figures in Viallanes final work I am led to accept his 

 bterpetation of these bodies, which he appears to regard as " annexed" to the cerebral lobes. A 

 t'^-eiarainatiou of my sections and of my figures, which, however, do not show so clearly as his 

 tl. X, Pig. 18, the entire stalk of the body, or its intimate connection at its base with the cerebral 

 lobes, leads me to adopt Viallanes view. At the same time there is a remarkable difference observ- 

 able between these mushroom or pedunculated bodies and those of insects and spiders, a difference 

 to which Viallanes does not refer. This stalk, however, is in part seen in the sections represented 

 by it'.y PI. XIV, Fig. 18, s^. III. b., where the stalk is seen to arise from the bulbous or lateral portion 

 of the cerebral lobes (h. c. /.), and to send off an ascending branch, and lateral branches. In PI. 

 XXXIV, the artotype from a inicrophotograph of the same section faintly represents the cerebral 

 h)bes, and the stalk of the mushroom body arising from the lateral or bulbous portion. 



We will first (1) consider their resemblance to the mushroom or pedunculated bodies of 

 insects; (2) their resemblance to or lack of resemblance or homology with the sti-atified body of 

 the Arachnid braiu; (3) their absence, i. c., the uiibranched and simple condition of the paired 

 cerebral lobes or ganglia in the freshly hatched Limulus larva. 



The mushroom bodies of Dujardin; the two mushroom bodies, with their stems, of Newton, 

 or the pedunculated bodies of Viallanes, and which I have, after Dujardin, called collectively the 



* In his last paper Viallanes regards this as the deutocerebriim. 



t Farther studies on the brain of LimuJiis pohiplieiniis. Zool. Anzeiger, 20 April, 1891. That the cheliceral 

 nerves are correctly named is doubtful. The so-i'aileil ihelicera in- first pair of appendages of Limulus may be 

 found to correspond to the antenna* or first pair of appeudages of the spider discovered by Jarpwo.sky, 

 S. Mis, 1G9 20 



