A Monograph on the Sub-class Cirripedia · Charles Darwin
CEMENTING APPARATUS.
Fig. 1 _a_, Basal membrane, with the cementing apparatus, of _Coronula balænaris_; a small portion of the parietal membrane, _p p p_, which coats the folded shelly walls, is left adherent to the basal membrane. _b_, the circumferential slip (shaded more darkly than the rest to catch the eye), separating the basal from the parietal membrane. _c′ c′_, slips of basal membrane, formed at each period of growth, and overlapping each other. _s s s s s s_, the six sutures in the walls, separating the six compartments, of which-- A is the basal margin of the rostrum, C C that of the lateral compartments, D D that of the carino-lateral compartments, and E that of the carina. _r_, _r_, rays or spokes of membrane, prolonged from the circumferential slip, and running under the trebly folded wall of each compartment, but here cut off; a similar ray should run under each line of suture (_s_). These rays, at their extremities, expand transversely; and the shape and length of the rays may be judged of from the basal outline of the folded walls given in Pl. 16, fig. 5. The two cement-ducts, proceeding from each cement-gland, debouch opposite the middle folds of the lateral (C C) and carino-lateral (D D) compartments. The layers of cement have been removed. N.B.
There is one considerable error in this figure, the two main trunks, connecting the cement-glands, and meeting at the centre, have been represented as forming a straight line, but in fact they form a very open angle, as is correctly shown in fig. 1 _c_. 1 _b_, Diagram, representing a vertical section through a portion of the basal and parietal membranes, with the thickness of the membrane enormously exaggerated. _z z z_, layers of cement, which, if the section had been made in the line of the cement-ducts, would have been seen proceeding out of these ducts, as is represented at (_t_), where the section is supposed to have taken the above course. _c′ c′_, the slips of basal membrane. _b_, the circumferential slip; beneath this the coarsely dotted layer represents the cement, lately excreted, and before it has acquired its proper transparent structureless character, elsewhere represented by fine dots. _p_, membrane externally coating the walls of the shell. _t_, cement-ducts opening beneath the basal membrane.
1 _c_, The central portion of fig. 1 _a_, considerably magnified. _c′ c′_, slips of the basal membrane; but the shell, when these were formed, was so young that the walls had not acquired their folded structure; in the centre the prehensile antennæ of the pupa may be obscurely seen. _f_, the main cement-trunk, connecting the cement-glands. _h_, a cement-gland, from which two cement-ducts proceed. _a a_, cement-ducts (cut off), leading to opposite the middle fold of the carino-lateral compartment. _b b_, cement-ducts (cut off), leading to opposite the middle fold of the lateral compartment. _a′ b′_, a pair of cement-ducts, with their orifices opening on the under side of one of the slips of basal membrane (_c′_), at a point which once was opposite the middle of the carino-lateral and lateral compartments. The orifices of the other ducts, towards the centre, may be seen forming straight lines. 2, Cement-ducts and one cement-gland of _Chelonobia patula_, represented without the basal membrane, to which they adhere: _f_, _f_, main cement-trunk; _g_, enlarged portion; _h_, gland; _a_, _b_, the two ducts proceeding from this gland, and bifurcating several times before debouching on the under side of the basal membrane. Several other cement-ducts, proceeding from other glands, are represented just as they appeared under the microscope.
3, Cement-ducts and glands of _Tubicinella trachealis_, represented without the basal membrane to which they adhered: (_f_) (_f_), main cement-trunk, connecting the several glands; _h_, cement-gland; _a_, cement-duct, with a singular loop (_a′_) having two projections or rudimentary branches; _b_, spur or rudiment of a second cement-duct; _c_, third cement-duct. 4 _a_, Chain of cement-glands of _Balanus tintinnabulum_, _with all the ducts removed_, _excepting those proceeding from the last formed gland_, which latter correspond in age with the last-formed zone of the shelly basis; the whole of the basis having been removed by acid. _f_, main cement-trunk connecting the glands. _gh_, last-formed cement-gland. _k_, _t_, two cement-ducts, proceeding from a great common duct; one of these bifurcates at (_t_), and one branch joins at (_t′_) the corresponding branch from the corresponding gland. _i i i_, circumferential duct, into which the ducts _k_, _k_, _t_, _t_, _t′_ all enter. _i′ i′_, branches proceeding from the circumferential duct, which branch and sub-branch till they form a sheet (_z z_) of cement-tissue on the outside of the basis of the shell. 4 _b_, two cement-glands of _Bal. tintinnabulum_ (this figure, to match with 4 _a_, ought to have stood upside down), taken from near the centre of the basis, greatly enlarged; (_f f_), main trunk; (_g_), enlarged portion of the trunk; (_h_), gland; _k_, _t_, two cement-ducts proceeding from a common point, one of them (_t_) bifurcates, and gives off a rudimentary branch, _t′_; _m_, a spur, or rudimentary duct. The gland, _h_, has been pushed on one side, it ought to lie over the enlarged portion (_g_). There is a considerable difference between these two glands and that (_gh_) represented in fig. 4 _a_; the neck of the gland in the latter being elongated into a great common duct, and the spur or rudimentary duct (_m_) being absent.
Text from Project Gutenberg, public domain in the United States.