119 



LIMULUS. 



LIMULUS. 



450 



assigned to them, in order that he might not break the connection 

 which unites all the Maxillated Crustaceans. 



The body of these animals is described by M. Milne-Edwards as 

 composed of three portions a cephalo-thorax, an abdomen, and a 

 tail : the two first portions are each covered by a horny shield, arid 

 the third assumes the form of a long stiletto. The cephalo-thoracic 

 buckler, which represents the carapace of Apia [BINOCULUS] and of 

 the superior Crustaceans, is the largest : it is convex above, concave 

 below, and rounded in front and on the sides, whilst posteriorly it is 

 deeply notched for the reception of the base of the abdomen. On its 

 upper surface is an unequal space, slightly or not at all convex, which 

 is circumscribed in front and on the sides by two curved crests, and 

 occupies behind the whole length of the straight portion of the poste- 

 rior border articulated with the abdomen. This space, which may ba 

 termed the occipital region, is subdivided longitudinally into three 

 lobes by two furrows which curve inwards anteriorly; and on the 

 median lobe may be also remarked a median ridge or elevation more 

 or less distinct, at the anterior extremity of which is a small smooth 

 tubercle having the aspect of a stemma, and on each side of which in 

 fact is a very small smooth eye. This conformation led Latreille and 

 others to attribute three stemmata to these animals. Towards the 

 middle nd on the outside of the lateral ridges which circumscribe 

 the occipital region on each side are situated the composite eyes, 

 which are of an oval form, and exhibit hexagonal divisions on their 

 transparent cornea. The anterior and lateral or marginal region of 

 the cephalo-thoracic buckler forms in front and on the sides a very 

 inclined plane, and presents nothing remarkable ; the only point that 

 requires notice is, that posteriorly it is prolonged beyond the occipital 

 region, so as to constitute on each side a sort of horn directed 

 backwards. 



The second buckler, or abdominal portion of the body, is much 

 less wide than the preceding, but long also, and of an inequilateral 

 hexagonal form, whose posterior border is more or less concave. Its 

 anterior border is articulated with the posterior border of the occipital 

 region of the carapac--, and its latero-anterior edges correspond to the 

 oblique borders by which the marginal region of the same buckler is 

 terminated behind. The latero-posterior borders, which are in general 

 longer than the preceding, form with these last a very obtuse angle, 

 and present a series of eight teeth separated from each other by six 

 depressions, in each of which is inserted a large moveable spine whose 

 point is directed backwards. Above, this abdominal buckler is convex 

 and divided into three lobes, of which the two lateral are very large, 

 and the median lobe narrowed behind and separated from the preceding 

 by two rows of small depressions. From the middle of the posterior 

 bonier of this second portion of the body springs a long styliform 

 piece, which, being situated above and behind the anus, should be 

 considered as the analogue of the caudal ring. 



On the lower aspect of the body appears anteriorly a flat and 

 triangular surface, which is on a level with the frontal border ; but in 

 the rest of its extent ihe cephalo-thoracic buckler is deeply excavated 

 for the lodgment of the feet These last immediately surround the 

 buccal aperture, and are so disposed that their basilary joint performs 

 the functions of the mandibles and jaws of the ordinary crustaceans, 

 whilst their internal branch is elongated in order to constitute an 

 ambulatory and prehensile member : there are six pairs of these feet. 

 The first, termed Mandibles by Fabricius and Latreille, and Palps by 

 Cuvier, are much smaller than tl:e others, and situated before the 

 mouth, near the median line : they are inserted on an unequal mem- 

 branous eminence which fulfils the functions of a labrum, and are 

 composed of three joints, the two last of which are disposed so as to 

 constitute a claw. The four following pairs of feet, or rather jaw- 

 feet, much resemble each other, and are each composed of six joints : 

 the first of these joints is very large, and terminates on the inside by 

 a lamellar prolongation, armed with strong spines, and performing the 

 function of a jaw : there is also, under its internal and anterior angle, 

 a small moveable piece. The succeeding joints constitute an elongated 

 and slightly-compressed foot; and in the females the penultimate 

 joint is prolonged below the last, so as to form with it a claw with 

 equal branches : this is sometimes the same in the male ; but in some 

 species of Limuli this sort of hand is wanting in the feet of the 

 second and third pair, the prolongation representing the immoveablc 

 finger not being developed. The sixth pair of feet differs much from 

 the preceding : their basilary joint is larger, terminates on the internal 

 ide in a toothed surface bearing some resemblance to that of a grind- 

 ing mandible, and carries at its external angle a flabelliform appendage. 

 Sometime* there exists a small lamellar appendage at the extremity 

 of the fourth joint, and .the next joint carries on its anterior border 

 many of those aubfoliaceous and elongated laminre which hide nearly 

 entirely the succeeding jaint, as well as the small didactylous hand which 

 terminates it. Lastly, between the base of these feet, at the posterior 

 part of the thorax, are two small lamellar pieces which are obtuse at 

 the end, and furnished with spines, which seem to be the vestiges of a 

 seventh pair of limbs. The abdomen is hollowed out into a rather 

 deep cavity, which is very analogous to that in Spharoma and mauy 

 other ftopoda. In this cavity are lodged the abdominal false feet and 

 the branchin> fixed to their posterior surface. There are six pairs of 

 these members, but the most anterior are not distinct, and are united 

 on the median line, so ag to constitute a great foliaceous and nenrly 

 BAT. BIST. PIT. TOL. III. 



circular valve, but which is truncated anteriorly, and which entirely 

 covers the succeeding false feet : in each half of this operculum are to 

 be distinguished one or two basilary pieces and two terminal lamina;, 

 which represent the two branches which ordinarily terminate these 

 organs : one of these pieces, situated near the median line, is small, 

 and separated from that of the opposite side by a fissure ; the other 

 is very large : finally, on the superior or posterior surface of this 

 first pair of false feet the two orifices of generation are found. The 

 succeeding false feet are equally foliaceous, and united on the median 

 line throughout the whole extent of their basilary piece ; but the two 

 branches which terminate each of these organs are free and more 

 developed. The internal branch is composed of two joints, the first 

 of which is quadrilateral and elongated, the second foliaceous and 

 oval. The external branch is represented by a very wide lamina, 

 which is rounded externally, and resembles that of the operculum. 

 The two external thirds of the posterior surface of the basilary por- 

 tion of these limbs are occupied by a great gill formed of a consider- 

 able number of laminse, or rather of cutaneous folds, disposed trans- 

 versely, and piled one on the other like the leaves of a book. These 

 leaves adhere to the false feet throughout the length of their base 

 or anterior border, and are free in the rest of their extent. They are 

 triangular, with a curved border, and increase in size from the upper 

 extremity of the branch to its base, so as to give to this last the form 

 of a pyramid, the posterior ridge of which is curved, the two free 

 surfaces convex, and the base rounded. The free edge of each leaf 

 is furnished with a small horny band destined to sustain it, but 

 throughout the rest of their extent these folds are membranous: there 

 are about 150 of them in each of the first pair of ^ills, and a few 

 less in the succeeding gills ; the last has only about 130. 



Limuhis Moluccanus, reduced onc-fourtli, and seen from above. 

 a, position of the two smooth eyes ; b, b, lateral composite eyes ; c, c, 

 respiratory aperture*. 



The mouth, situated towards the posterior third of the lower 

 surface of the cephalo-thoracic buckler, is surrounded, as has already 

 been noticed, by the feet, the basilary joint or haunch of which is 

 armed with spines or teeth and disposed so as to serve for the work 

 of mastication. This aperture is infundibuliform, and continued 

 with the digestive tube, which is directed at first directly forward, 

 then curves upwards and backwards, and proceeds in a direct line to 

 the extremity of the abdominal buckler, where it presents anew a 

 small curvature in its course to the anus. The first portion of this 

 canal, directed forwards and situated below the intestine, constitutes 



2o 



