28 A. S. PACKARD, JR., ON THE ANATOMY 



hardened and after remaining twenty-four hours in gum water, in a mixture of equal parts 

 of paraffine, wax and olive oil, so that the consistency of the imbedding substance was 

 nearly as soft as the tissue to be cut. The sections were made by a microtome devised by 

 Mr. Mason, and were mounted in glycerine jelly. 



While between two hundred and three hundred sections wei'e made, by fir the 

 best results were obtained by a series of fifty-six sections, cut by Mr. Mason from one 

 brain, and forty-four from the upper four-fifths of another brain, the slices being either 

 TTo ^^' 5^0 of an inch in thickness ; the best results of course were obtained from 

 the thinner sections. These were deejjly stained of a dark-brown, the ganglion-cells and 

 nerve-fibres being much lighter than the nucleogenous masses forming the larger part 

 of the brain, these being dark brown, the former tawny or yellowish brown. 



The examination of a few sections of the brain of the lobster and the locust also kindly 

 prepared by Mr. Mason, enabled me the more readily to understand the recent papers of 

 Dietl, Newton and Krieger on the brain of the crawfish and insects, and afforded a stand- 

 ard of comparison with which to study the topography and histology of the brain of 

 Limulus. 



General anatomy of the brain. The position of the bi-ain in relation to the body 

 walls and digestive tract is seen in the section of the adult animal on plate 2, fig. 1, br. 

 The central nervous system consists of an oesophageal collar made up by the consolidation 

 of six pairs of postoral ganglia from which nerves are distributed to the six paii's of 

 gnathopods. The ring is closed in front by the supra-oesophageal ganglion, or the 

 partial homologue of that pair of brain-centres in the normal Crustacea and Insects. It 

 will be remembered that in these Arthropods the brain is situated in the upper part of the 

 head, in a plane parallel to, but quite removed from, that of the rest of the ganglionic 

 chain ; in Limulus, however, the brain is situated directly in front of and on the same 

 plane with the horizontal oesophageal collar, and the abdominal portion of the central 

 nervous system. 



We now come to the singular relations of the ventral system of arterial vessels to the 

 nervous system. This is fully described by A. Milne-Edwards. After describing the 

 vascular ring surrounding the oesophagus he remarks : " Lorsqu'on ouvre cette portion 

 du systeme arteriel, on trouve dans son interieur le collieur nerveux oesophagien, le reste 

 de la chaine ganglionnaire et la plupart des principaux nerfs qui y sont baignes par le sang. 

 Les arteres ne sont par seulement appliquees sur le systeme nerveux, comme chez les 

 scorpions, ou deveioppees a la surface de ce systeme de fa(^on a le recouvrir ; elles logent 

 celui-ci dans leur cavite. Cette disposition rappelle celle du reservoir sanguin dans 

 I'interieur duquel M. de Quatrefiiges a constat^ I'existence des ganglions cerebroides chez 

 les Planaires, et celle du vaisseau ventral des Sangsues, decouvert j^ar Johnson." He then 

 states that these singular relations of the apparatus of innervatiou with the arterial system 

 of Limulus have been seen, but very incompletely, by Professor Owen, and are more 

 intimate than this eminent anatomist thinks, and quotes as follows from Owen's 

 Comparative Anatomy and Physiology of Invertebrate Animals (1855, p. 320) : " The two 

 large lateral branches (celles qui j'appelle les crosses aortiques) form arches which curve 

 down the side of tlie stomach and the oesojjhagus, giving branches to both those parts and 



