- Fig. [6], [Proteolepas bivincta]: diagram, showing the probable position of
the young animal, just before its metamorphosis, within the carapace of the supposed pupa; a, caudal appendages; b, six pairs of natatory thoracic legs; c, mouth, no doubt closed and functionless, as in other pupæ; g, threads of attachment, with cement-ducts in process of formation; h, antennæ. - [7], [Proteolepas bivincta], magnified about twenty-six times.
- m, mouth, the summit being formed of the labrum and palpi joined.
- 1c, first segment of body; homologically the seventh or last cephalic segment.
- 2t to 8t, second to eighth segment of body; homologically, first to seventh thoracic segments.
- 9a to 11a, ninth to eleventh segment of body; homologically, three segments of abdomen.
- d′, three muscles attached on each side to the labrum, and running to the gnathites.
- e e, great ovarian sack.
- f, true ovaria.
- g, threads of attachment.
- h, three terminal segments of the antennæ of the pupa.
- i, vesicula seminalis.
- k, papilla representing the penis.
- Fig. [1], [Balanus tintinnabulum]: an enlarged longitudinal section
through the shell and sack, with the right-hand scutum and tergum and right-hand half of shell and basis removed, exhibiting the body of the animal not in section. The cirri are exhibited only on one side. - A, A, orifice of shell, within which lies the operculum formed by a pair of scuta (S), and pair of terga (T).
- B, basis (homologically the anterior end of the shell).
- K, carina of shell (or dorsal valve or compartment of shell).
- K′, sheath of carina.
- L, lateral compartment of shell. The carino-lateral compartment is hidden by the scutum and tergum.
- R, rostrum of shell (or ventral valve or compartment of shell).
- R′, sheath of rostrum.
- O, O, opercular membrane, connecting the opercular valves with the overhanging basal edge of the sheath.
- S, scutum.
- T, tergum.
- a, adductor scutorum muscle, with the scutum on the near side removed.
- b, the whole space enclosed by a broken sinuous line, round a and b, shows the cut surface of attachment to the near scutum, which has been removed.
- b′, lower muscle, on the near side, running from near the basal edge of the scutum to near the basal margin of the labrum (e). Above this are three other muscles (all on the near side), running to the membrane between the labrum and adductor muscle.
- c, prosoma, including the main portion of the stomach and thickened ends of the vesiculæ seminales: homologically this is formed by the development of the second thoracic segment, which carries the first pair of cirri; and possibly, in part, by the antecedent segment, i. e. the first thoracic segment.
- c′, thorax, extending from the prosoma to the posterior end of the body: the letter (c′) stands on the segment supporting the third cirrus; homologically, this segment is the fourth thoracic.
- d′, orifice of the acoustic sack, above which is the basal articulation of the first cirrus.
- e, labrum, forming the back (i. e. anterior end) of the mouth, with the transverse palpi obscurely seen on the summit.
- f, sack in which the animal lies, with the tunic lining it, continuous with that investing the prosoma (c), and lining the under sides of both opercular valves, but cut off round (b) and (a) by the removal of the near scutum. The branchia on the further side, which occupies the position represented at fig. 3, is covered by the body of the animal.
- g g, ovarian, inosculating cæca, branching from the simple duct (of which the near one of the pair is represented), leading to the ovaria (not represented) within the body.
- h, rostral depressor muscle of the scutum: the lateral depressor muscle of the scutum is hidden by the body and by the membranes of the sack.
- i, carinal depressor muscle of the tergum.
- z, antennæ (three terminal segments) of the pupa; I distinctly saw these in this species, but they are here represented considerably too large, even on the supposition that a young shell had been drawn, and magnified about twelve times.
- [2], Testes of [Balanus perforatus], greatly magnified.
- [3], Branchia of [Bal. tintinnabulum], on the same scale as in fig. 1, and in its natural position. This drawing was made by lifting up the body in fig. 1; the organ being thus completely exposed over its whole interior surface; a is the basal end of the spur of the tergum.
PLATE [26.]
STRUCTURE OF THE MOUTH AND THORAX.
N.B.—The same letters of reference are used for the parts of the mouth throughout this plate. All the organs here represented have been cleaned by boiling in potash, and consist exclusively of the external membrane.
- Fig. [1], Mouth of [Balanus perforatus], viewed from vertically above,
with the first pair of cirri x x in their proper position, cut off close above their basal articulations. - a, outer maxilla; a′, ditto, cut closely off.
- b, maxilla.
- c, mandibles.
- d, palpus; d′ ditto, cut closely off.
- e, labrum, crest of.
- x x, first pair of cirri, cut off.
- [2], Supra-œsophageal cavity of the mouth of [Balanus improvisus], torn open, with the palpi, mandibles, and maxillæ removed, exhibiting the inner face of the labrum, laid flat, and the inner faces of the outer maxillæ; scale as in fig. 1.
- a, outer maxillæ; a′′, inner and lower lobe of ditto.
- d′, point of attachment to the torn-off palpus.
- e, labrum, crest off; e′, central notch, with graduated teeth on both sides.
- f, triangular thickened portion of the inner fold of the labrum; f′, rib or bar of membrane, thickened to support the surrounding very thin membrane of the supra-œsophageal cavity.
- g, opening of the œsophagus.
- h, forked bar of thickened membrane, for same purpose as f′.
- [3], Mouth of [Coronula balænaris], divided vertically in a transverse line, with the outer and inner maxillæ and mandible on the left side removed, with the labrum, the other mandible and both palpi viewed on the inside, and with the œsophagus adherent in its proper position.
- c, Mandible, upper free segment; c1, second or middle segment; c2, supposed third or basal segment, forming the basal margin of the mouth, but not separated by any articulation from the labrum.
- d d, palpi; d′, aperture, through which the inside of this palpus can be seen, caused by the mandible having been cut off; the membrane on the under side of this aperture is thickened, and affords the chief support to the palpus; d′′, thin membrane, apparently part of the palpus, connecting the attached basal end of the palpus to the externo-lateral surface of the mandible.
- e′, central notch in the crest of the labrum; e′′ e′′, basal margin of the labrum, to which the membrane of the body is joined.
- f, thickened portion of membrane, part of the inner fold of the labrum, corresponding with f in fig. 2.
- g, orifice of the œsophagus, with the front part of the supra-œsophageal cavity cut away; g′, lower, expanded, or bell-shaped, end of the œsophagus, in its natural condition.
- i, k, concavities for the attachment of muscles running to the mandibles.
- m, cut off edge of membrane forming the side of the mouth, which cut edge can be followed up above the aperture d′, where the upper basal end of the palpus has been cut off, and so onwards by g, to the mandible on the opposite side of the mouth.
- [4], Mouth of [Coronula balænaris], viewed from the outside, in front, with the inner maxilla, mandible, and palpus on the left side of the figure, and nearly the whole labrum, and the greater part of the palpus on the right side, all cut away. The maxilla, mandible, and basal portion of the palpus on the right hand, are pulled out of their proper positions; for the toothed edge of the mandible ought to have stood higher, and nearly in a line between and behind the outer maxillæ, and then the basal margin e′′ of the lateral portion of the labrum would be raised, and curling round, would stand nearly where the letter b′ is now placed.
- a a, outer maxilla, upper free lobe; a′′, lower and inner free lobe; a1, supposed second or middle segment; a2, supposed third or basal segment; a′′′, basal articulation of mouth, separating it from the ventral surface of the thorax.
- b, inner maxilla; b′, apodeme of do.
- c, mandible, upper free segment; c1, second segment; c2, third and basal segment, but not separated by an articulation from the labrum.
- d, palpus; d′′, membrane uniting the basal end of the palpus, where attached to the labrum, to the side of the mandible.
- e′′, basal margin of the labrum, on one side, displaced and pulled down.
- n, orifice of the olfactory pouch.
- [5], [Balanus amaryllis]: mandible, upper free segment, seen from the side that faces the labrum; p, an arched line, where the thickened membrane of the upper free part terminates, and is united by thin membrane to the near side of the palpus; q, ligamentous bands for the attachment of muscles.
- [6], [Balanus amaryllis]: palpus, on the same scale as the mandible, fig. 5, seen from the outside, so that the further or under face is the side which, towards the right hand, is united to the near face of the mandible, fig. 5; r, long bristles, springing from a protuberance near the extremity; these bristles, in many species, form a long single row, parallel to the basal margin; s, upper row of shorter bristles; t, row of very short bristles, arising from the further side and curling over the crest of the labrum.