. A text-book of invertebrate morphology. Invertebrates. TYPE CRUSTACEA. 373 manner tlie grasping claws (Fig. 165, B) or chelae are devel- oped by the flexion of the terminal joint on the subterminal or by the elongation of the angles of the latter into a more or less strong process against which the terminal joint may be approximated. The description given above of the various appendages is of course general, the modifications found in the various forms being almost endless. Indeed in parasitic forms the ap- pendages, except those concerned in mastication, may entirely disappear, all gradatio
. A text-book of invertebrate morphology. Invertebrates. TYPE CRUSTACEA. 373 manner tlie grasping claws (Fig. 165, B) or chelae are devel- oped by the flexion of the terminal joint on the subterminal or by the elongation of the angles of the latter into a more or less strong process against which the terminal joint may be approximated. The description given above of the various appendages is of course general, the modifications found in the various forms being almost endless. Indeed in parasitic forms the ap- pendages, except those concerned in mastication, may entirely disappear, all gradations between fully-developed append- ages and the merest rudiments being found in various Fig. 166.—Sixth {A) akd Sbcond (5) Thoracic Appendages op Bkanchio- POD, Apus (after Zadsacb from Bronn). br = bract. fl = flabellum. 1-6 = inner lobes. From what has been said, however, it may be seen that typi- cally the Crustacean appendage may be considered a biramous structure, consisting of a two-jointed basal portion termed the protopodite and two jointed branches termed the exopodite and endopodite (Fig. 165, ex, en) according to their relation to the median axis of the body. Additional rami are frequently developed upon the protopodite—such, for example, as that termed the epipodite (Fig. 167, ep) and the branchia (br). How- ever, although such a limb may be considered typical, it is not necessarily also the most primitive. Indeed when the simplest forms, such as the Phyllopoda, are examined it will be found that the more posterior appendages have a very different composition. Thus in the genus Apus the sixth thoracic appendage (Fig. 166, A) consists of a central two-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original McMurrich, J. Playfair (James Playfair), 1859-1939. New York, H. Holt and Company
Size: 1831px × 1365px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1894
