Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/692

Rh 658 CRUSTACEA 18,250,000 annually. March to August is the period of greatest catch. 1 The river cray-fish, Astacus fluviatilis (fig. 25), also common to the rivers of Europe, is largely caught, and when fresh boiled is not to be despised. It is largely imported into London, and is used by the chefs at the West End to garnish dishes. The writer with a friend caught as many as 900 cray-fish in a single evening from 8 till 12 (with a series of simple scale-like nets baited with liver), along the bank of the Thames and Severn Canal, Gloucestershire. The Murray river cray-fish from Australia (Potamobius serratus) is as large as a fine sea-lobster, and has its segments ornamented with spines, reminding one of the spiny lobster 2 (Enoplodytia s^lssexiensis) from the chalk of Sussex and Kent. 3 More than fifty genera of fossil Macroura have been met with and described ; the earliest known is the Anthra- ]&amp;gt; daemon Grossartii from the Lower Carboniferous series near Glasgow. Similar forms have been obtained from the Coal-measures in England; from Illinois, U.S. ; from L ^hernia, etc. I. PODOPHTHALMIA : (2.) SioMAPODA. All the members embraced within the three divisions of the preceding order (Decapoda) were cryptobranchiate, in this order they are nudibranchiate, i.e., the gills are composed of plates or simple filaments attached to the feet, whilst the carapace, so largely developed in the order Decapoda. is here both shorter and nar rower, and the body less com pact. Taking Squilla (fig. 71) as an example, the segments are much less coalesced than in the lobster. Those bearing the eyes and the antennules are read ; ly separable from the front of the head, and are not covered by the carapace, which only con ceals eight segments, whereas in the lobster it covers fourteen, and in the crab twenty-one. The gills are borne by the ab dominal swimming feet, free and uncovered. The first pair of thoracic limbs are developed into a pair of large and formid able claws, the terminal joint of which bears a row of long, sharp, and recurved teeth ; these double back upon the edge of the penultimate joint which has a groove to receive them, like a pocket- comb. In Mysis, &quot;the opossum shrimp,&quot; another member of tins order, the two posterior pairs of feet only are branchi- f jrous ; all the feet are biramous and flagellate ; in the female the hinder feet are modified into broad plates which, uniting beneath the body, form a pouch or marsupium in 1 Lobsters are sent alive to the London market, packed in damp sea weed, moss, or heather, from Stornoway in the Island of Lewis, from Ireland, Scotland, the Orkneys, the south coast, and Channel Islands, and from Norway. Fishermen and salesmen are said to know the south coast, Cornish, Scotch, Irish, or Norwegian lobsters at sight, just as cattle salesmen know a &quot;Hereford&quot; or &quot;Devon,&quot; a &quot;Scotch&quot; or &quot; Irish &quot; beast. The largest common lobsters weigh from 8 to 12 Tb. But the great lobster of the American coast (largely imported in tins into Europe) weighs more than twice as much. 8 Dixon s Geology of Sussex, tab. 38, figs. 6, 7. 3 For the numerous species of Palcemonidas belonging to this division, we must refer the reader to Bell s British Stalk-eyed Crustacea, to Dana s magnificent volumes and atlas on the Crustacea found during the United States exploring expedition, and to De Haan s Fauna Japonica, aad Milne-Edwards s Hist. Nat. des Crustacees, Fig. 71. Squilla mantis, Rondel. ; south coast of England and Medi terranean. which the eggs arc protected and the young pass through their infancy. 4 These opossum-shrimps, which are pelagic in their habits, are frequently met with in countless myriads towards the surface of the Greenland Sea, and, though small, they form the chief part of the food of the common whale (Baloena mysticetus)^ Some forms of Erichthys are included in this divi sion; these, like Mysis, are also pelagic, and occur abundantly on the surface of the Indian and Atlantic Oceans, where, together with the larvae of Cirripedes and many other oceanic cosmopolites, they may be taken with the towing net in abundance. Numerous specimens of true Squilla (Sculda pennata, Munst) and of a Mysis-like Crustacean have been found fossil in the Solenhofen limestone, of Oolitic age, in Bavaria. With the Stomapoda are also placed a group of very anomalous and larval-looking Crustacea (the Diastylidm) originally noticed in 1843 by Mr Harry Goodsir, who obtained them from the Firth of Forth. They closely re semble Copepoda in aspect, and might readily be confounded with the larval stages of some Decapod. They have, however, been found with their eggs borne by the female in an incubatory pouch beneath the thorax, as in Mysis. The branchiae are situated on each side of the thorax im mediately above the insertion of the legs, and approach in their comb-like appearance to those of the higher Crustacea. Three genera have been established for these singular forms, namely, Cuma, Alauna, Sodotria (see fig. 36). II. EDRTOPHTHALMiA:(3.)IsopODA. From the stalk-eyed Podophthalmia we pass now to the sessile-eyed Edrioph- thalmia, in which the eyes with one exception are fixed immovably on the surface of the head. As in the higher forms, the eyes are compound, consisting in the young of some ten or twelve lenses only, but in the adult of as many as sixty to eighty. In nearly all, the body is distinctly divisible into three parts the head usually very small, the seven thoracic segments well and evenly developed, the ab dominal somites more or less coalesced. The general con formity in size and function of the thoracic somites and their seven pairs of legs characterizes the majority of the Isopoda. These legs are nearly uniform, and are fitted either for walking or for swimming, or as powerful hook- like organs to enable them to adhere to the fishes on which they are parasitic. The branchiae in this order are trans ferred from the thoracic legs to the abdominal appendages, which are converted into special organs of respiration. One group of Isopods, the Oniscidce (forming Spence Bate s and Westwood s family ^Erospirantia), familiar in our gardens under the names of &quot; woodlouse, &quot; &quot; sow-bug,&quot; and &quot; armadillo &quot; (fig. 22), are all air-breathers, incapable of existing in water, but breathing air which, however, it is necessary must be saturated with moisture. Several of the species which inhabit caves are destitute of eyes (e.g., Titandlies albus, Schrodte). The &quot;great sea-slater : (Ligia oceanica) is common on all our coasts, running with agility and feigning death when attacked. The genus Armadillo, found commonly in our gardens and woods, and so called from the perfect way in which the segments roll together, forcibly reminds one of &quot; the great Barr Trilobite &quot; (Illvenus Barriensis], from the Silurian of Staffordshire (7 in fig. 73). A very interesting little Isopod (presented to the British Museum by Dr Milligan of Tasmania), from Flinders Island, Bass s Straits, and named in MS. by 4 An allied species to Mysis, Thysanopoda (obtained in myriads by Couch on the Cornish coast from the stomachs of mackerel), carries its eggs, as does Cyclops guadricornis, in two bag-like ovaries depending from the posterior thoracic somite (Bell s Brit. Stalk-eyed Crust.) 6 Otho Fabricius, Fauna Groenlandica, p. 245.