A Monograph on the Sub-class Cirripedia · Charles Darwin
CIRRI AND LARVÆ, FIRST STAGES.
Fig. 1, Sixth cirrus of _Balanus amphitrite_ (_var._ cirratus), showing the muscles. _a_, _b_, flexor and extensor muscles, moving the upper segment (_i_ to _k_) of the pedicel. _c_ and _d_, flexor and extensor muscles, apparently moving the lower segments of both rami, as a whole; the lower articulations in these rami being confluent. _e_ and _f_, flexor and extensor muscles extending up both rami (those only in the near ramus being figured) to their tips. _g_ _g_, flexors of the separate segments in both rami. _h_, basal articulation of lower segment of the pedicel. _i_, upper articulation of lower segment of the pedicel. _k_, upper articulation of upper segment of pedicel. 2, Fourth cirrus of _Acasta sulcata_. _i_, upper articulation of the lower } _These two letters segment of pedicel. } apply to all the _k_, upper articulation of the upper } figures 1 to 6._ segment of pedicel. } _l_, curved teeth on the pedicel. _m_, " " on the segments of the anterior ramus. 3, Third cirrus of _Chthamalus antennatus_. 4, Second cirrus of _Balanus perforatus_, viewed exteriorly and laterally. 5, Third cirrus of _Xenobalanus globicipitis_. 6, Sixth " " " 7, Spermatozoa (copied from Mr. C. Spence Bate, in 'Annals and Mag. of Natural History' (S. 2), vol. viii, Pl. VIII). _a_, of _Verruca Strömia_, in an early condition. _b_, of _Balanus balanoides_, more mature. _c_, of _Balanus perforatus_, apparently mature. 8, Larva of _Scalpellum vulgare_, immediately after coming out of the egg, seen on the ventral surface (letters of reference given below). 9, Larva of _Balanus balanoides_, immediately after coming out of the egg, seen on the ventral surface, copied from Mr. C. Spence Bate's drawing in 'Annals and Magazine of Natural History' (S. 2), vol. viii, Plate VI, fig. 1 (letters of reference given below). 10, Larva of _Chthamalus stellatus_, after the first moult, but during the first stage, seen on the ventral surface, copied; with some alterations, from Mr. C. Spence Bate's drawing in 'Annals and Magazine of Natural History' (2 Ser.), vol. viii, Plate VIII, fig. 13.
(_The following letters apply to above figs. 8, 9, 10._) _a_, eye. _b_, first pair of antennæ, not observed in fig. 9. _b′_, the same antennæ, as yet encased (in fig. 8) within small horns. _c_, horns, including the second pair of antennæ. _d_, mouth, probosciformed: in fig. 8, the specimen having been acted on by potash, the œsophagus can be seen within, with the orifice beneath the swelling, which latter perhaps answers to the labrum. _e_, first, uniramous natatory leg (homologically the second thoracic limb). _f_ _g_, second and third, biramous natatory legs (homologically the third and fourth thoracic limbs.) _h_, posterior point of carapace. _i_, forked terminal projection of the body or abdomen. _l_, second forked projection. _m_, two sharp points, apparently representing a third forked projection. _n_, a rounded swelling, apparently lying between the carapace and the supposed abdomen, and believed to form the anus.
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