According to Sars, the 1 In Huxley's terminology the first two or three joints of the stem constitute a "protopodite," from which spring the "endopodite" and "exopodite."
- Amid the great variety of forms assumed by the appendages of the Crustacea, it is possible to trace, more or less plainly, the modifications of a fundamental type consisting of a peduncle, the protopodite, bearing two branches, the endopodite and exopodite.
In many cases, one of the branches, generally the endopodite, is more strongly developed than the other.
Thus, in the thoracic limbs of the Malacostraca, the endopodite generally forms a walking-leg while the exopodite becomes a swimmingbranch or may disappear altogether.
The two distal endites are regarded as corresponding to the endopodite and exopodite of the higher Crustacea, the axis or corm of the Phyllopod limb representing the protopodite.
It is not altogether easy to recognize the homologies of the endites and exites even within the order Phyllopoda, and the identification of the two distal endites as corresponding to the endopodite and exopodite of higher Crustacea is not free from difficulty.
The jaws have the gnathobasic endites developed at the expense of the rest of the limb, the endopodite FIG.
In the Malacostraca, the antennules are often biramous, but there is considerable doubt as to whether the two branches represent the endopodite and exopodite of the other limbs, and three branches are found in the Stomatopoda and in some Caridea.
In the Malacostraca they are chiefly sensory, the endopodite forming a long flagellum, while the exopodite may form a lamellar " scale," probably useful as a balancer in swimming, or may disappear altogether.
The endopodite, when present, is unsegmented or composed of few segments and forms the " palp," and outwardlydirected lobes representing the exopodite and epipodites may also be present.
Protopodite, endopodite, exopodite, and epipodite were considered to be the morphological units of the crustacean limb.
The endopodite (corresponding to the fifth endite of the limb of Apus, see fig.
(4) Three of the rami of the primitive limb (endites 5 and 6, and exite I) specially developed as endopodite, exopodite, and epipodite - the first two often as firm and strongly chitinized, segmented, leg-like structures; the original axis or corm reduced to a basal piece, with or without a distinct gnathobase (endite i)- typical tri-ramose limb of higher Crustacea.
(5) One ramus (the endopodite) alone developed - the original axis or corm serving as its basal joint with or without gnathobase.
(6) Two rami developed (usually, but perhaps not always, the equivalents of the endopodite and exopodite) supported on the somewhat elongated corm (basal segment).
The endopodite may be retained as a small segmented palp at the side of the gnathobase or disappear (mandible of Crustacea, Chilopoda and Hexapods).
It is by the specialization of two " endites " that the endopodite and exopodite of higher Crustacea are formed, whilst a flabelliform exite is the homogen or genetic equivalent of the epipodite (see Lankester, " Observations and Reflections on Apus Cancriformis," Q.
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