Note 156 — Order III.—APODA.

Any one who has not specially attended to the metamorphoses of ordinary cirripedes, who looks at the imaginary figure of the young Proteolepas, will feel much surprise at the relative positions of the parts; for the mouth and the first and even second segments of the body stand posteriorly (i. e. above in the figure) to the succeeding segments of the body, in relation to the carapace of the pupa; but this is only in accordance with the remarkable change in position (as explained in the introduction, p. 123, pl. 30, fig. 2), amounting almost to inversion, which the whole thorax of every young cirripede undergoes within the pupa, whilst the anterior cephalic portions and general covering are developed conformably with the pupal carapace, whence it arises that the dorsal surface of that part of the thorax immediately succeeding the mouth becomes attached to the ventral internal surface of the carapace. I believe that the peculiar flattened dorsal outline of the first two segments of the body of Proteolepas is due to these parts having been formed in contact (as represented in pl. 25, fig. 6) with the straight ventral surface of the carapace of the pupa. To place the young Proteolepas, and at the same time the carapace of the pupa, with all the parts in proper homological sequence, it would be necessary to seize the posterior end of the abdomen (a), and pull till the dorsal surfaces of the first and second segments of the body, separated from the ventral internal surface of the carapace, and stood posteriorly (i. e. above in figure) to the mouth, which latter would thus also have to rotate a quarter of a circle, so that the orifice would come to be directed outwards. Then every part would stand, in accordance with the archetype crustacean structure, in due order; but the three confluent anterior cephalic segments, forming the front part and carapace of the pupa, would, as in the case of all cirripedes, be of disproportionately large size in relation to the rest of the body.