MKMOIIIS OF TIIK NAIIONAL ACADKMV OF S( 1 KNCKS. 313 



XI. NoTKSilN Till; l-.MllKVoNlf UKVKI.Ol'M KNT OK TIIK ItltAIN AND VKNTU A I. CORD. IM-ATKS XVIII 



AND XIX. 



Tlio }i('iu'ial miirplidlojiv ol' tin- hniiii of liimiiliis can not ho with certainty I'lilly worked out 

 without a kuowicduc of tlio eiul)i\olo;;y of tlu- ncrvou.s system, especially of the relations of tlie 

 ncuroineres of the head and of thechaiifies which lake plaee in the relative arian},'einent of these 

 neuioiueres. and of the lolies forineil by them during the dovelopuient of the parts of tlie head in 

 the later embryonic stages. 



Also, the mode of development of the rutHo-like mas.ses of chromatic or aprotoplasmic •^-.uia- 

 lion cells will have to be studied dnrin',^ the period of larval life succeediiiij the lirst molt, and l)e- 

 fore (he body becomes, say, about an inch in leiifjth without the caudal spine. With the results 

 of Prof. Patten's work we are not satistied, as we feel by no means sure that his diagrams in his 

 Figs. 7, S, !), ami 10, however ingeni(ms, are in all respects reliable, and are eontident that no more 

 than a single pair of meilian eyes actually exist in nature. We hav(^ found no trac<;s of a second 

 pair of median eyes, nor has Kishinouye detected them. Until, then, Prof. Patten publislies his 

 observations in full we should prefer to wait before entirely accepting his diagianimatic figures 

 and some of the views expressed in his paper. 



The most important observation on the development of the brain of Limulus are those of Mr. 

 Kishinouye, who seems to have i)aid special attention to this subject. He states: 



The latenil lialve.s of tlir lU'ivmis sy.sti'in develop imlopenilently of eai-h otiicr. Eaih Iialf of the l)raiu with its 

 rorrespomliiij; voiitral iiorvc vdvA is proiliicod as a continuous long cord of epiblastic thickening just inside the 

 base of the appendages (Figs. 12-14). It is easy, however, to distinguish the Iirain from the ventral nerve cord. 

 When they .ire first formed, the former is very much broader than the latter, occupying almost the whole of the 

 segment of the cephalic lobe, while the ventral nerve cord occupies only about one-third of the breadth of each 

 appendage-bearing segment (Fig. 12). 



Kishinouye then describes the "paired .small invagination" which appears in the lateral part 

 or margin of the brain, and another paired epiblastic invagination along the anterior internal 

 corner of the margin of the brain. These cephalic invaginations are, however, very shallow, and 

 disapi)ear before the separation of the nervous system from the epiblast takes place. 



]iortions of these lobes belong to the lobes in question. . I had regarded them as lateral lobules of the cerebral lobes, 

 but now accept Viallanes' view as to their nature. 



M. Viallanes has also succeeded better than myself in making a wax model of the interior structure of the brain, 

 giving adorsal, ventral, and a sagittal view, and I reproduce his figure of the model of the dorsal view a,s it shows 

 better than I could do the relation of the optic and ocellar lobes to the cerebral lobes. I am able to confirm the 

 accuracy of his work, and am glad to bear tribute to the skill and patience he, has shown in working out the struc- 

 ture of the brain of this animal. On i)agi's 449 and 450 he discusses the organizatii>n of the l)rain of Liunilus and 

 of Arachnids. He very briefly (in three lines) states his belief that the twopeduuculated bodies of Limulus are the 

 homologues of the "striated organ," of Arachnids, but does not enter into details, <u- attempt to show how the two 

 bodies in Limulus can be liomologized with the single stratified organ of Arachnids. Neither does he refer to the 

 very great <liffercnces between the size and shape of the cerebral hemispheres of Limulus and Arachnids, and to 

 other difterences to which I have drawn attention. I can not agree with AL Viallanes that the brain of Limulus 

 is the exact hom(dogue of the brain of Arachnidcs; I hold that the "deuto cerebrum" does not form a part of the 

 lirain proper, that it is not fused with it, that it is post or at least par.otcsophogeal, since it innervates the first jiair 

 of appendages, and this shows that Limulus is in this respect more primitive than the Arachnids. The fusion of 

 what were originally distinct ganglia (see my PI. XVIII, Fig. 7) has never gone on so completely as in the .Arachnids. 

 Hence the brain characters, together with the absence of the urinary tubes, and of trarheje, and the presence of 

 branchiie, besides the shape of tht- six pairs of cephalic appendages and the large median eyes, as well as other 

 minor characters, are sufficient in importance to make Limulus the representative of a class by itself, with which 

 the trilobites should be associated. 



1 may be alli>wed to add that M. Viallanes' contem|>tuoas critique of my first very imperfect account of the 

 brain of Limulus, ]iublished in 1>«0, is a grain harsh and unfair, since before writing it he must have had in his hands 

 my brief abstract of the prejient jiajier published in the Xoologischrr Ait^ciifer for April 20, 1891, and a copy of which I 

 maih'd to him. Even in my first account published in ISHO, whih' I incorrectly stated that the braiu was uusymmet- 

 rical, I called attention to and figured the " nucleogenous bodies, " and pointed out their enormous development. To 

 my discovery of thi-se important structures M. Viallanes condescends to make no reference; I had also pointed out 

 the differences between the large ganglion cells and the small aprotoplasmic ones, or the "nuclei "composing the 

 nucleogenoous bodies. I did not point out dearly the limits of the median and lateral eye lobes, and those of the 

 cerebral lobes, b--cans'- in niy ofmic acid preparations (ma<le in 1879) they are not shown so well iis in those stained 

 with carniiuc. , 



