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The following abstract is the result of farther observations based on 

 transverse, longitudinal (sagittal), and horizontal sections of the supra- 

 oesophageal ganglion, or brain, belonging to adult individuals about 

 eight or ten inches in length , exclusive of the caudal spine. The 

 transverse and sagittal sections were stained with haematoxylin , the 

 horizontal with carmine 2 . 



The most striking histological feature of the brain is the immense 

 development and singular arrangement of the convoluted, ruffle-like 

 masses forming the thick layer of »nucleogenous bodies«, as we have 

 called them, and which form the cortex of the cerebral and other lo- 

 bes, and which enclose masses of myeloid or punctured substance. 

 These appear to be simply nuclei, but when they are scattered they 

 are seen to be ganglion cells. They are the ganglionic nuclei of Dietl, 

 and »cellules chromatiques« of St. Remy :$ , and as he describes in the 

 brain of Myriopods and Arachnida, readily take a deep stain, thus con- 

 trasting with the unstained , white punctured substance of the lobes, 

 and origins of the nerves. The enormous development of these chro- 

 matic cells , and their grouping into such a great number of nucleo- 

 genous bodies or plates is a peculiarity of the brain of Limulus. 

 Another characteristic of the brain of Limulus as compared with that 

 of other Arthropoda, including the Scorpion, is the remarkably small 

 number of the normal ganglion cells. 



In its shape and gross anatomy, the brain of Limulus, as we for- 

 merly stated, differs fundamentally from that of Arachnida, in sending 

 no nerves to the first pair of appendages, the only nerves arising from 

 the brain being those distributed to the median and lateral eyes, and 

 to the integument, the »nerfs tegumentaires frontaux« and »nerfs tegu- 

 mentairesfronto-inferieurs« of Milne Edwards. The bminof Limulus is 

 thus homologous with the portion of the brain of spiders and scorpions 

 situated in front of the origin of the so-called mandibular or cheliceral 

 nerves, and which is the »forebrain« of Professor Patten. In the adult 

 brain of Limulus, as seen externally, the largest nerves are those sent to 

 the lateral eyes, and which arise very near the upper surface of the brain, 

 one on each side of the median furrow. Below is the origin, in the 

 median line , of the , for the middle and larger part of its course , un- 

 paired nerve te the median eyes. A little below, but in about the 

 upper third of the brain-mass, arise a pair of frontal, tegumental ner- 

 ves, and directly below them are the descending fronto-inferior tegu- 

 mental nerves. No nerves arise from the lower half of the brain, which 



2 The brains were prepared, cut, and mounted in balsam by Prof. H. C. 

 Bum pus. 



3 Archives de Zool. exp. et gén. 2e Ser. T. V. bis. Suppl. 1887. 



