PROFESSOR OWEN ON LIMULUS POLYPHEMUS. 20& 



give a rich display of arterial ramifications. But dissection showed that the contents of 

 the seeming arteries ceased to be the simple injected matter where the ' gastric arches ' 

 (ib., s) reached the nervous ring (ib., /3) ; for here the coats of the artery become thinned, 

 the injection lining them as a thin flake of colouring matter, and, at the same time, 

 covering a thinner membrane which formed the ' neurilemma ' or chief layer of the deli- 

 cate tunics of the nervous matter of the neural ring. 1 The same condition was presented 

 by the seeming abdominal arterial trunk continued backward from the neur-arterial circle 

 (PL XXXVI, a, B, to or of nerve n 19). On slitting open the coats of the blood-vessel 

 and washing out the flake of injection, the ganglionic nervous chord was exposed in its 

 interior. 2 The same result followed the like perquisition of the smaller ramifications of 

 the vascular system into which the injection had penetrated, and engendered the conviction 

 that the main pair of arteries had but a brief course as such, 3 becoming resolved on 

 reaching the neural ring into blood-sinuses, a condition which prevails throughout a great 

 proportion of the vascular system of Limulus. The whole nervous system, save where 

 the terminal twigs are lost in the tissues, is bathed in the blood of these sinuses, which 

 retain the appearance of ramified vessels, through their relations to the nerves as the 

 vascular envelopes of these. 4 Elsewhere the sinuses expand, lose the character of tubes, 

 or vessels, occupy the interspaces of viscera and muscles, initiate the ramified branchial 

 system of vessels, and finally return the blood to the pericardial-like sinus enclosing the 

 heart. 



" A pair of arteries is sent off near the anterior pair of ostia, and are closely connected 

 with the much larger veins emptying the neighbouring sinus into the corresponding parts 

 of the pericardial one. These arteries pass outward and forward, and subdivide into 

 branches, which are lost upon the epimeral nerves. I was unable to distinguish an artery 



1 " Preparation No. 1303 c, Physiol. Series, Mus. Coll. of Surgeons." 



2 " The neurine thus seems to be small in proportion to the thick neurilemma, as Gegenbaur remarks^ 

 but he did not recognise the share taken by the arterial tissues in this sheath : — ' Bezuglich des feineren 

 Baues soil die schon oben angefuhrte dicke Umhullung des Schlundringes erwahnt werden, derzufolge 

 der eigentliche Nerventheil des Schlundringes relativ klein erscheint,' op. cit., p. 241." 



3 " They are shown as cut off from the arches and lost upon the brain in PI. XXXVI." 



4 " This interesting stage in the differentiation of nerves and vessels was demonstrated in my 

 Hunterian lectures of 1852, 'Organisation of the Entomostraca illustrated in the Limulus,' Lecture XVI, 

 Crustacea, 'Synopsis,' March, 1852, and is briefly enunciated in the volume on Invertebrata as follows: 

 — * The sides of the great oesophageal ring are united by two transverse commissural bands ; but the most 

 remarkable feature of the nervous axis of this Crustacean is its envelopment by an arterial trunk. A pair 

 of aortse from the fore part of the heart arch over each side of the stomach, and seem to terminate by 

 intimately blending with the sides of the oesophageal nervous ring. They, in fact, expand upon and seem 

 to form its neurilemma ; a fine injection thrown into them coats the whole central mass of the nervous 

 system with its red colour,' ' Lectures on the Comparative Anatomy and Physiology of the Invertebrate 

 Animals,' by Prof. Owen, F.R.S. (2nd edit., London, 1855, Lecture XVI, p. 310). Gegenbaur, in his 

 historical treatise on Limulus (op. cit., p. 241), remarks: — ' Auch die peripherischen Nerven sind 

 sammtlich von einer dicken Hiille umgeben, die sogar noch makroskopisch erkennbar ist.' " 



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