298 ZOOLOGY. 



ages are of uniform shape like legs, not like mandibles oi 

 maxillae, and are adapted for -svalking ; the feet are pro- 

 Tided with, sharp teeth on the basal joint for retaining the 

 food. The mouth is situated between the second pair ; the 

 first pair of legs are smaller than the others. All end in 

 two simple claws, except the sixth pair, which are armed 

 with several spatulate appendages serring to prop the crea- 

 ture as it burrows into the mud. The males differ from the 

 females in the hand and opposing thumb of the second pair 

 of feet. These cephalo-thoracic appendages are quite as dif- 

 ferent from those of most Crustacea as those of the mites 

 and spiders, wliich have a pair of mandibles and maxiUse, 

 the latter provided with a palpus. Appended to the ab- 

 domen are six pairs of broad swimming feet, all except the 

 first pair of which bear on the under side two sets of about 

 one hundred respiratory leaves or plates, into which the blood 

 is sent from the heart, passing around the outer edge and 

 returning around the inner edge. This mode of respiration 

 is like that of the Isopods. 



The alimentary canal consists of an oesophagus, which 

 rises directly over the mouth, a stomach lined with rows of 

 large chitinous teeth, with a large conical, stopper-like valve 

 projecting into the posterior end of the body ; the intestine 

 is straight, ending in the base of the abdominal spine. The 

 liver is very voluminous, ramifying throughout the cephalo- 

 thorax. The nervous system is quite unlike that of the 

 Crustacea ; the brain is situated on the floor of the body in 

 the same plane as the rest of the system, and sends a pair of 

 nerves to the compound cye=. a sinde nerve supplying the 

 ocelh.* The feet are all snppliel with nerves from a thick 

 ring surrounding the resnphagus. The nerves to the six 

 pairs of abdominal legs are sent otf from tlie ventral cord. 



* The nervotis system of lamulus is quite unlike that of the Scorpion, 

 where the brain is situated in the upper part of the head and supplies 

 the maxillje with nerves, and is situated directlv over the infracEso- 

 phageal ganglion ; and, besides, there is no oesophageal rinor as in 

 Limulus, only the two commissures connecting tlie brain with tlie 

 lufraoesophageal ganglion as tisoal in the Crustacea and Arachnida ic 

 general. 



