Miscellaneous. 153 



1855, Professor Owen inserted in his ' Lectures on the Anatomy of 

 Invertebrata ' various facts with regard to the structure of these 

 singular Arthropoda ; and quite recently an English journal an- 

 nounced that this illustrious naturalist had resumed the investigation 

 of the same subject; but his work is as yet known only by an 

 abstract published in 1871. Some points relating to the histology 

 of the Limuli have been treated by M. Gegenbaur ; and works of 

 great interest on the habits of these animals, on their embryology, 

 and on their zoological affinities, have been published by MM. 

 Lockwood, Packard, Dohru, and E. van Benedeu. Einally, Mr. 

 Woodward, in several consecutive memoirs, has presented us with 

 very interesting observations upon the relations of the LimuU with 

 the Trilobites, the Pterygoti, and various articulate animals, the 

 remains of which occur in the fossil state in the Silurian, Devonian, 

 and Carboniferous formations. 



1 have no intention of discussing here the questions relating to 

 the zoological affinities which may exist between the Limuli and the 

 extinct species of ancient geological periods. My observations relate 

 to the anatomy of these animals, and principally to the constitution 

 of their circulatory apparatus and to the structure of their nervous 

 system. 



The circulatory apparatus of the Limuli is more perfect and 

 complicated than that of any other articulate animal. The venous 

 blood, instead of being diffused through interorganic lacunae, as in 

 the Crustacea, is for a consideralle portion of its course enclosed in 

 proper vessels with walls perfectly distinct from the adjacent organs, 

 originating frequently by ramifications of remarkable delicacy, and 

 opening into reservoirs which are for the most part well circum- 

 scribed. The nutritive liquid passes from these reservoirs into the 

 branchiae, and, after having traversed these respiratory organs, 

 arrives, by a system of branchio-eardiac canals, in a pericardiac 

 chamber, then penetrates into the heart, of which the dimensions 

 are very considerable. It is then driven into tubular arteries with 

 resistant walls, the arrangement of which is exceedingly complex, 

 with frequent anastomoses, and of which the terminal ramifications 

 are of marvellous tenuity and abundance. By making use of the 

 microscope we can trace them, wdth their contours still well defined, 

 even into the substance of the finest and most transparent mem- 

 branes (for example, the intestinal coats and even the floor of the 

 pericardiac chamber) ; we see them also, by employing sufficient 

 magnifying-power, in the midst of the primitive muscular fibres, 

 which th(^y do not even equal in diameter ; and some of those which 

 I measured had a calibre of less than -pi-jy millim. 



One of the most striking pcculiariti( s of this vascular apparatus 

 consists in its rehitions with the nervous system. Thus the ab- 

 dominal artery, formed by the union of the two aortic branches, 

 ensheathes the whole of the ganglionic cluiin : most of the nerves 

 are lodged in the branches which spring from this median vessel. 



These relations of tlie apparatus of innervation with the arterial 

 system of the Limuli were perceived, although very imperfectly, by 



