LlMULUa 



LIMULUS. 



it is narrow, rather long, and furnwlied internally 

 with longitudinal plait*. The atomach ia repreaented by the curved 

 ami anterior portion of thia aame tube ; it ia email and directed 

 vertically ; ita walla are very fle*hy , and puckered (fronceea) internally ; 

 aa internal furrow aeparatea it from the ceaopbacua, and iU pyl>rie 

 xtrmity advance* in form of a cone in the cavity of the inteotiue, 

 ao aa to constitute a apeoiaa of ralvulr. The third portion of the 

 iaUatiaal tab* oocupiee nearly the whole length of the body, and 

 repreMtnU the duodenum, or ohylifio ventricle: it U cylindrical, 

 Anight, and baa toward* ita two extremities some transverse folds of 

 the internal membrane, and more or leas projecting papilla?. On each 

 aid*, a little above the level of the mouth, are two small circular 

 orifice*, which belong to the biliary apparatus, and ita posterior 

 ittvmity i *uddenly contracted in order to ita continuation with the 

 fourth |>ortiou of the digrative tube, which may be considered as the 

 iateaiinuui rectum. It ia very abort, plaited longitudinally in ita 

 interior, and curved downward* at ita extremity in order to reach the 

 anu*, which i* *ituated in front of the inwrtiou of the caudal sword. 

 The liver 611* in the cophalo-thoraz the apace situated between the 

 inteatine and the muscles of the fet : it extends also into the abdo- 

 men, and ia oompowd of blind and contorted canals, which are oon- 

 tinurd with the excretory conduit*, the four trunks of which open 

 in the anterior part of the duodenum. 



I. l*miJmt rWOTtamU. MO from below. , fronll portlnn of the tanu 

 pew ; . aalcriof frt ; , anoail pair of fn-t ; t, ilxth pair of fret ; r, ibdomen ; 

 /, o*mUr Umln. forawd bjr IB* nrt pair of filM frrt, *nd rnminf thr 

 natkUrnnn r*M ; ?. braa*hl, or gttU , *, c.od.1 .Ijlrt, or xiphoid proem. 

 MU*j*-Kd aid*. 



. * of ta* Mwond pair of jaw.frrt. Milrw.fxl.nrd.. 



. OM W ta* WCUMI pair of J.w.fm la a male /.;*; Hnl<uc<u. Mllnr. 



. OM f the W.m-h.frrna. f*jM frt. *, hnncblv. 

 . 0|ii>i*l>r IMBIM ef Uw (bdoKnt Km on It* Intmul *aif*cr, and .how 

 Ike orUka* f ta* erfaa* W (*a*r*Uo. Mila*-K<]..ul.. 



The heart bean much resemblance to that of the f-'yttilltr. [STOMA- 

 FODA.] It ia a long dorsal veaael with flethy walla, which present on 

 each aide aeven transverse aperturea furuiahed with valvulea, and 

 which give origin to various arteries. 



The nervou* system consist* in a medullary ring which surround* 

 the oywphagua, gives origin to the cephalo-thoracic nerves, and i con- 

 tinued back wards with a stout cord, from the posterior part of which 

 the abdominal nerves spring. 



The organs of generation open externally by the aperturea at the 

 base of the first pair of false feet. In the female theae orifices each 

 communicate with an oviduct, which when Arrived in the thorax ia 

 divided into two branches, the ramifications of which constitute the 

 ovary and embrace the liver. In the male, in place of the vulva:, 

 thero is a small cylindrical penis. (' Histoire Naturelle des Crustacea/ 

 1640.) 



Such ia the statement given by M. Milne-Edwards of the organisa- 

 tion of this highly interesting form. 



Professor Owen, in his ' Hunteriau Lectures' (1343), ha* drawn 

 attention to certain points in the structure of these animals. 

 He states that the Xijiliosura, typified by the Ltmuliu, or 

 Molucca Crab, have the head and thorax more completely blended 

 together than in the true crabs, which they resemble in the general 

 form of the body ; but that they are peculiarly distinguished from all 

 other Criutacra by having the office of jaws performed by the first 

 joint of the thoracic legs, which surround the mouth. The large 

 cepholo-thoracic segment is, he remarks, protected above and laterally 

 by an expanded crescentic shield obscurely divided by two longitudi- 

 nal impressions into three lobes, supporting the organs of vision on 

 their highest port The tergal parts of the segments of the second 

 division of the body are also blended, he observes, into one trilobate 

 clypeiform piece, their original separation being indicated by the 

 branchial fissures, and the number of the segments by that of the 

 lamelliform appendages attached to their inferior surface. The termi- 

 nation of the intestine beneath the last segment of the second division 

 of the body of the Limului proves, in Professor Owen's opinion, 

 that division to answer to the abdomen in the MaJacoKraca ; but 

 admitting the sessile eyes to indicate a distinct segment, not more 

 than sixteen segment* can, he remarks, be determined by the 

 appendages to enter into the composition of the entire crust of the 

 Limulut, including the sword-shaped appendage, which is analogous, 

 in the Professor's view, to the last or post-anal segment of the 

 higher Cnutacea, and consists of a single modified segment. 



Professor Owen then advert* to the small Entonwutraca, in which 

 the number of the thoracic and abdominal segments generally exceeds 

 that in the Malarottraca, and adduces, aa an example, the Sranchiput 

 (Chiroctpltalut) itaynalu [BBANCHIOPODA ; ('iiiuoiK.rii.ujV, which baa 

 eleven thoracic segments and nine abdominal or caudal rings, besides 

 a distinct head protected by a thoracic shield. In the Itanrn, in which 

 this shield is developed, as in Cyprit, Daphnia, and other Knlonuatraca, 

 to the extent and in the form of a bivalve shell enveloping the whole 

 luxly, the number of thoracic and abdominal segments exceeds, ho 

 remarks, twenty-four. 



These observations relative to the segments of the Cruttacta are 

 interesting when considered with reference to a race of that class of 

 which no living analogue exists ; and he thus points out the value of 

 this part of their conformation as applicable to the subject : 



" The distinction between the Knlnmotlraca and the Malacostraca 

 in the number of the segments of the body is of the first importance 

 in MI ti-riuining the affinities of the ancient extinct CYtufocro called 

 TnlMla. These remarkable animals were nlinost the sole repre- 

 sentatives of the present class in the periods which intervened between 

 the deposition of the earliest forailiferous strata to the end of the 

 Coal Formation. They appear to have been without antenna; and 

 feet ; the structure of the tergal part only of their body-segmenta ia 

 yet known ; but these are grouped together to form a distinct head, 

 thorax, and abdomen or tail. The bend is formed by a large semi- 

 circular or creaoeut-shaped shield ; the thorax consists of from ten to 

 fifteen segments, and the abdomen or tail includes at leaat eight 

 segments in this Vaiymene (Prep., No. 208), in which it is bent under 

 the thorax, as in the Crab ; the abdomen, post-abdomen, or tail, as 

 the third segment is variously termed, contains fifteen fettered seg- 

 menta in Aiu;,/,ui caudalut : the segments of both thorax and 

 abdomen are very similar to each other, and gradually decrease in 

 lice. They are divided by two longitudinal furrows into three lobes. 

 The head support* a pair of large compound eyes situated near the 

 side*, like the large outer pair of eyea in the Limultu, which they 

 resemble in form and structure. . 



" The Maltuottraca are divided into two groups, according to the 

 attachment of the eyes : those with immoveable aeasile eyes form the 

 Kdriopklhalna ; those with moreable pedunculated eye* the J'oilnjili- 

 (halma. 



" The lower organised or Edriophtholmous forms of Malacostracoua 

 Crmlacta resemble the TrilobiUt in the non-confluence and uniformity 

 of the aegmenU of the thorax and abdomen. Certain genera, aa 

 Serolu and Eojiyrtu, have the tergal arc* of the segment* trilobed ; 

 but they exceed not the characteristic number in the Matacoilraca, 

 : and the aevt-u rings of the thorax are clearly indicated in each by the 

 seven pain of articulated feet which they support, although these are 



