Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/695

Rh CRUSTACEA 661 fewer and less varied forms of Trilobites. Those in the Carboniferous belong nearly all to two genera (Phillipsia and Griffithides), both small, neat, and simple forms. None are met with in rocks of later date. IT. EDRIOPHTHALMIA : (5.) AMPHIPODA. This order, as Spence Bate has well observed, constitutes a group among the Edriophthalmia, parallel with the Macroura among the Podophthalmia, whilst the Isopoda may represent the broad and flattened Brachyun, the Caprellae offering a kind of parallelism with Squilla and its allies. As in the Isopoda, the head is small and carries only the organs of sense and nutrition ; the sessile eyes 1 are generally small, yet in a few instances they are extremely large (e.g., Lestri- ffonus and Thaumops), covering the entire sides of the head. The seven thoracic segments, constituting the middle-body, are well developed and nearly equal in size ; all the seg ments are compressed laterally as in the Palcemonidce. The two anterior pairs of the seven thoracic legs (see Th. 8, 9 in fig. 1), which are jaw-feet in the Podoph thalmia, are here developed into arm-like legs, having, an enlarged penultimate joint or hand, against which the seventh and terminal joint doubles back, like a finger against the palm, and so forms a prehensile organ similar in form to the claws in the Crangonidce. The best-formed claws are seen in Orchestia Darwinii (fig. 45), and in Melita exilii (fig. 7G). Fie. ~C,.-MeHta exilii, n. sp., male, enlarged five times. The large branchial lamellae are seen projecting between the legs. (Fritz Miiller.) The ova are nourished within a pouch formed by a series of foliaceous plates attached to the four anterior pairs of legs ; except in the Hyperiidce, which are parasitic on Medusae, as already mentioned. The males in the Amphipoda closely resemble the females (save in those forms in which the hands are enlarged in the male), but contrary to the general rule the females are much smaller than the males. This division, like the preceding one, has its ter restrial representatives, Talitrus and Orchestia, the &quot;sand- hoppers,&quot; 2 living out of the sea, but choosing moist places. Orchestia with us loves to live within reach of the sea spray, but some species in the southern hemisphere (0. tahitiensis, telluris, and sylvicola) live many miles inland, some under plants at an elevation of more than a thousand 1 The outer integument of the eyes is never divided into facets, except in the Hyperiidce. In many of the Phoxides the eyes appear to l&amp;gt;e wanting ; but this is probably caused by the absence of any colouring pigment. In Niphargus the eyes are obsolete or rudimentary. In Ampelisca they appear like four simple organs resembling the ocelli of true insects (Spence Bate and Westwood, Brit. Scss. Crust, vol. i. p. 4). _ 2 It is in the summer months that they occur in such vast myriads npon our sandy shores. At Whitsand Bay Mr Twain saw &quot;not millions, but cartloads,&quot; of one species (Talitrus locmta) lying piled together along the margin of the sea. They devour offal of every description, including dead carcasses of animals, which they rapidly assimilate and remove. In their turn they afford a repast to the ring- plover, the common wood-pigeon, and numerous shore-birds which rapidly devour them, as well as some coleopterous insects (the Cillenum lateral? and roscus cephalotes (Bate and Westwood). feet above the sea. But by far the largest section are natatorial in their habits, being most active and untiring swim mers. One form, Gammanis pulex (fig. 77), is most com mon in our freshwaters, two other genera, both blind, Niphargus with three species, j ri ,t~ FIG. 77, Gammarus. sp.. fresh water and Crangonyx, with one species, are found in wells in England, 3 and from their struc ture there is every reason to conclude they are as truly indigenous to these xxnderground water-courses in the Chalk, Oolite, or Carboniferous Limestone, as are the numerous species of blind Crustacea met with in the waters flowing through the Mammoth Cave, Kentucky. A curious subdivision of Amphipods is formed by the Podocerides (Amphithoe and Podocerus), all the species of which invariably construct nests in which they take shel ter and nourish their young. These abodes are built of wood or stones, mud, clay, &c., united together by a cement excreted by the animals themselves. Some closely resemble miniature birds -nests, others are in the form of tubes. This division includes another most destructive wood- borer, the Chehira terebrans, so devastating to piles and submarine timber all round the shores of Europe, but not record ed from other lands. Finally, we come to the minute aberrant forms of Didichiidce and Ca- prellidae (fig. 78), in which the body is reduced to a slender elongated Cylindrical FIG. :8.Caprel!a tulcrculata, Guerin ; south form, the. thorax hav- coast % &amp;lt; Spence Cttte &amp;gt; ing only about six somites (one being absent and two soldered together), and the abdomen being quite rudi mentary. They have long antennae and feet, all fitted for climbing and holding on by. Their singular appearance has caused them to be called &quot;fspectre shrimps.&quot; With these aberrant forms are associated the Cyamidce (fig. 79), a family which affix themselves by their strong recurved legs to the rough portions of the Cetacea upon which they feed. The feet are all prehensile ; the third and fourth somites bear the *- branched or simple branchiae. The abdomen, as in the Ca- prellidce, is rudimentary ; the eggs and young are sheltered Fja -&amp;lt;,._,, 6 CyamM nomr&amp;gt;son ^ by four broad lamellar plates, G. 0f:s e fomtd attached to ffwrnxxfon -, i j r btdent, Portland Roads. 2, v uyaunis developed from the append- m?M,Vau*eme; found attached to a^es on the under side of the common whale. (Sptnce Bate.; O body of the female. Spence Bate and Westwood have figured five species. They approach in many respects to the Pycnogonidcie, which also live parasitic on Cetacea (see ARACHNIDA, vol. ii. p. 276-77), but we must not attempt to discuss their affinities here. A fragment of a presumed Amphipodous Crustacean has been described by the writer from the Upper Silurian (the Necrcgammarus Salweyi) another, the Gampsonyx fmlriatns, occurs in the Coal- measures of Germany, Bohemia, and America. Mr Spenco Bate has described one from the Permian of Durham, the Prosopomscus problematicvis, its modern living representa tive, the Sidcator, making peculiar tracks upon our shores to day like those met with upon the surfaces of slabs of 3 Spence Bate and Westwood (Sessile-eyed Crustacea, vol. iii. p. 811-328).