ZOOLOGY. 



the King Crabs or Molucca Crabs (Ltmulus) 

 which sometimes measure two feet in length 

 The dorsal surface of the cephalo-thorax is coverec 

 by a large convex shield, upon which are placec 

 the eyes. The abdomen is also protected by a 

 second shield, which terminates in a long sword- 

 like process. The mouth, placed on the under 

 surface of the head, is surrounded by six pairs o: 

 appendages, whose bases are suited for masticat- 

 ing food, their extremities being clawed. Attached 

 to the abdomen are six pairs of appendages, which 

 carry the gills. 



SUB-CLASS Malacostraca includes those crus- 

 taceans which have a definite number of body- 

 segments. It includes 



DIVISION (A). EDRIOPHTHALMATA, 



in which the eyes are not situated on stalks, and 

 the body is unprotected by a shield. It comprises 

 three orders. 



ORDER 8. Lcemodipoda 

 (laimos, the throat, pous, a 

 foot). The head is confluent 

 with the first thoracic segment. 

 These segments support the 

 four anterior feet, so that they 

 seem to be under the throat 

 hence the name. The abdomen 

 is rudimentary. The most 

 common is the Cyamus Ceti 

 (or Whale-louse), which is a 



Cyamus Ceti. 



small animal parasitic on the body of the whale. 



ORDER 9. Amphipoda (amphis, on both sides, 

 and pous, a foot). The respiratory organs are 

 attached to the thorax ; the abdomen is well 

 developed, and composed of seven segments. 

 The first thoracic segment is distinct from the 

 head, and the thorax carries seven pairs of limbs, 

 some of which are directed forwards, some back- 

 wards. The species best known in Britain is the 

 Talitrus locusta (Sand-hopper), which burrows in 

 the sand, and seldom enters the water. 



ORDER 10. Isopoda (isos, equal, and pous, a 

 foot). The head is distinct. The feet are alike, 

 and adapted for locomotion and grasping. The 

 most familiar is the Oniscus (Wood-louse). 



DIVISION (B). PODOPHTHALMIA. 



The eyes are supported on movable stalks, and 

 'ie cephalo-thorax is protected by a carapace. It 

 includes two orders. 



ORDER u. Stomapoda (stoma, a mouth, and 

 pous, a foot). They are all marine. The Locust- 

 shrimp (Sguilla), which is common in the Medi- 

 terranean, is a well-known form, and is about 

 seven inches long. The gills are naked, and 

 adhere to five pairs of feet, which are abdominal 

 in position, and leaf-like in form. Some of the 

 anterior appendages are transformed into power- 

 ful, prehensile feet, but they are never used for 

 nipping, while the posterior feet are used for 

 swimming. 



ORDER 12. Decapoda (deka, ten, pous, a foot). 

 It includes the stalked-eyed crustaceans, whose 

 cephalo-thorax is protected by a strong calcareous 

 carapace, which exhibits no trace of segmentary 

 division. The gills lie in a cavity on each side of 

 the cephalo-thorax. The thoracic legs are ten in 

 number, hence the name. It includes a great 



number of species, most of which are useful for 

 food, and they are by far the most highly organ- 

 ised of all the Crustaceans. According to the 

 development of the abdomen, three sub-orders are 

 formed. 



Sub-order i. Macrura (makros, long, oura, a 

 tail), or Long-tailed Decapods including the 

 Lobster, Prawn, Cray-fish, and Shrimp. The 

 abdomen is well developed, and ends in a powerful 

 fan-shaped swimming organ. The head carries 

 the compound eyes, placed on long movable 

 stalks. Two pairs of antennae are also present 

 The mouth is on the under surface of the head, 

 and some of the appendages are so modified as 

 to form powerful claws or nipping organs. The 

 abdominal segments carry swimming organs. The 

 heart is well developed, and is situated dorsally. 

 The nervous system is well pronounced, and is 

 situated ventrally. 



Sub-order 2. Anomura (anomos, irregular, and 

 oura, a tail). The abdomen is not so long as in 

 the Macrura, nor so short 

 as in the next order. To 

 this order belongs the 

 Hermit Crab (Pagurus), 

 whose abdomen is quite 

 soft. They are remark- 

 able for living in the 

 deserted shells of mol- 

 .usca, exchanging a less 

 : or a larger as they in- 

 crease in size. It fixes 

 tself in the shell by a 

 sucker and rudimentary 

 feet Well-developed feet 

 are present, the anterior 

 mir being usually trans- 

 "ormed into formidable nippers. They feed upon 

 dead fish. When alarmed, they retire within the 

 shell, and close the aperture with their claws. 



Sub-order 3. Brachyura (brachys, short, oura, a 

 ail), or Short-tailed Decapods have the tail 

 short, and folded under the large cephalo-thorax. 

 The Large Edible Crab (Cancer pagurus) is the 

 ype. The legs are of moderate length, but the 

 claws are large. At low tide in summer, it is 

 "ound in holes of rocks. The Small Edible Crab 

 Carcinus mcenas) is another well-known British 

 species. The Land-crabs (Gecarcinus) called also 

 iolet crabs and white crabs, from their colour 

 are natives of the West India Islands and South 

 America. They have an arrangement of leaflets 

 "or retaining moisture for their gills. They live in 

 mountainous places, far from the sea, which they 

 /isit once a year to deposit their eggs. During the 

 lay, they retire into their burrows, which they make 

 n the earth, roaming about at night in search of 

 ood. The Common Crab, on coming out of the 

 egg, has a long tail, with several curious spine- 

 ike processes attached to it, and was formerly 

 [escribed as a distinct animal under the name of 

 Zoea. It undergoes curious metamorphoses before 

 t reaches the adult condition. 



CLASS 2. Arachnida are annulose animals, 

 whose respiration is aerial. The head is con- 

 uent with the chest, thus forming acephalo-thorax, 

 nd the abdomen never carries jointed append- 

 .ges. Eight legs are present, but the antennae as 

 uch are absent. It includes the familiar group 

 f Spiders and their allies. 



143 



Hermit Crab in shell 



