J96 



NATURAL HISTORY. 



abdomen is fully developed but has no appendages. Nothing can well be imagined more diverse than 

 the zoea, nauplius, and adult stages in the life history of this Prawn. 



Although the young of nearly all the Crustacea pass through numerous moults before altaining 

 the adult state, yet, even after maturity, the shelly envelope is not permanently retained, but is 

 exuviated and renewed as often as the growth of the animal necessitates its enlargement. By this, 

 wonderful provision the otherwise inelastic corselet is prevented from interfering with the continued 

 growth of its wearer. The process of moulting is exactly analogous to the shedding 'of the skin and 

 scales in reptiles. In insects as all know who have kept silkworms this moulting takes place 

 several times in the grub or larva before it finally arrives at the perfect state. It then occurs no. 

 more. Insects, therefore, cannot grow after they reach the imago, and their life is consequently soon 

 ended. Crabs, on the contrary, go on moulting and growing larger for many seasons, and each year 

 they lay their eggs, so that they are more prolific, although less highly organised, than the insect 

 tribe. The manner in which Crabs cast off their old shell is very singular, usually without producing 

 any change in their external form, and when they have quitted the old habitation the whole body is 

 already covered with a new suit of armour, which is, however, still soft, and does not acquire its 

 requisite solidity for some hours, or even days after the operation. 



The Crustacea also possess the power of reproducing injured or lost limbs; if one or mor& 

 distant joints of a limb be torn off, the animal has the power of throwing off the remainder of the 

 limb. This separation always takes place at the base of the first joint. The perfect restoration of' 

 the liinb is not effected at once. After the first moult a new limb is produced of diminutive size. 

 After a second, the new limb is veiy nearly twice as large as at the first, and at the third it 

 advances nearly to its natural bulk and form. It is said that the noise of a thunderstorm or the 

 discharge of a cannon will cause Crabs and Lobsters to throw off their claws ; the same effect is also- 

 produced by the infliction of any sudden injury. The Broad-clawed Porcelain Crab (Porcellana-. 

 platycheles), if seized by the claw, will leave it behind him and beat a retreat without it. 



The accompanying table may serve to convey a general notion of the Crustacea as a class. 



CLASS CRUSTACEA. 



DIVISIONS. 



I. THORACIPODA.- 



Special locomotory organs <( 

 belonging to the thorax. 



I 

 f3. 



PODOPHTHALMIA. Eyes on mov- 

 able foot-stalks. Branchiae 

 proper almost always present. <! 

 Thorax covered more or less 

 completely by cephalic shield. 



OEDEKS. 

 ^"o-g ( a, BRACHYURA. (Short-tailed. ) Crabs. 



o.|"^ b, ANOMOURA. (Various-tailed.) Heraiit; 

 1. < S,'5 ! Crabs. 



O eS 



n > 3 j <", MACROURA. (Large-tailed.) Lobsters- 

 Shrimps. 



II. GNATHOPODA. 



Limbs nearly always be- 

 longing to the head, but 

 not generally specialised, , 

 as their bases perform the ' 

 part of jaws. Branchiae 

 usually exposed and 

 aiding in natation. 



m. ANCHORACEPHALA. f>. 



Adult (female) attached J 

 by the head, and perma- . 

 nently fixed. 



l -2. STOMAPODA. (Mouth-footed.) -Squilla, Mysis, &c. 



EDRIOPHTHALMIA. Eyes fixed, f ., T ,_, 



Branchi* formed of modified i 3 " Ib ^ DA ' (Equal-footed )-Wood Lice, Omtnu. 

 appendages. Limbs usually { ' 



seven ]>airs. No cephalothoracic I 4. AMPHIPODA. (Both feet. ) Sand-hoppers, TuLtrim,. 

 carapace. ( Gammarus. 



MEROSTOMATA.-The mouth fur- , 5> XlPHOSURA. (Sword-tails. )-King Crabs, Limning 

 nished with mandibles and i 



maxillae, the terminations of i G. (El'RYPTERlDA. Extinct.} Eurvptcrm, Pten/yotus r 

 which become walking or swim- [ & c . 



(7. (TRILOBITA. Extinct. ) Trilobites, Calymene, Pha- 

 BRAN-CHIOPODA. Most of the CO P S > &c - 



appendages, save those of the ,8. PHYLLOPODA. (Leaf-footed.)-^4/)iw, rancki(n: r 

 head and mouth, converted into j &c. 

 lamelliform branch^. | 9 CLADOCERA. (Branched horns.)- Water FU8, 



(_ Daphnia, &c. 



LoPHYROPODA.-Locomotory or . ,10. OSTRACODA. (Shell-covered. }-Cypr, 

 gans having stiff ?:airs. Branchiae-; 



attached to mouth organs. j 11. CoPEPor.A. (Oar-footed )Ci/dops, 



[. CetochUas, &c. 



f!2. RHIZOCEPHALA. (Root-headed.) Parasitic forms - 

 CIRRIPEPIA. Adult animals per- ! Peltoc/aster, Sacculina, &c. 

 manently attached to some living , 



or dead object. Sexes usually < 13 BALANID.E. (Acorn shells. )-Balanus, Coronula, 

 united. | 



I 14. LEPAPID.-E. (Barnacles.) Lepas, Scalpettum, 



1. PoUicipes, &c. 



