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Show 1880.] OF T H E M A L E O F SPIRULA AUSTRALIS. 353 fundibular characters of the female Spirula ('Annals,' &c, p. 4) are repeated in the male, as, for example, the long, narrow, articular cavities (Plate XXXII. fig. 4, k) receiving the corresponding prominences (ib.l) on the juxtaposed inner surface of the mantle, and the small terminal valvular aperture (m). The chief sexual modifications affect, as usual, the brachial part of the head. The three pairs of the ordinary arms (Plate XXXII. figs. 1 and 5, l, 2, 3) spring from little more than the dorsal half (fig. 5) of the brachiophorous part of the head. The ventral portion (fig. 6) is mainly occupied by the expanded bases (t, t') oi the tentacles (t), which form oblique cavities, or short sheaths, lodging the modified ventral (4th) pair of arms (ib. 4, 4.) The specimen here described presented at first view, from the ventral aspect, a single clavate process (ib. fig. 2, 4) in the place, apparently, of the fourth pair of arms-the process ascending for a length of 10 millims. between the bases of the tentacles (t), and its own base being united by a pair of short webs to those of the arms of the 3rd pair (ib. 3, 3). From the dorsal aspect of the specimen (ib. fig. 1) the clavate process, 4, presented a longitudinal cleft near one side, marking off the portion 4' (fig. 6). Divaricating this portion, it was seen to be a distinct though smaller clavate process (fig. 4, 4'), compactly adherent to, but not organically connected with, the larger one, though springing in close contiguity therewith, from the ventral brachiophorous portion of the head (ib. fig. 6, 4, 4'). It was now plain that these clavate processes were the sexually modified homologues of the 4th pair of ordinary arms in other Cephalopods. Each was subquadrate in shape, the side of the longer process lodging the shorter one, being hollowed to receive it. The end of the shorter process (4') was truncate, as if a part had been broken off; that of the longer process was rather enlarged, terminating obtusely, and supporting a small accessory protuberance (fig. 6, 4, p). Longitudinal and transverse sections displayed a solid fibrous tissue in each: the fibrillae of the smooth-muscular type were arranged in a thin outer layer of transverse fibres, and, in a larger proportion, of inner longitudinal fasciculi, offering in transverse section the radiate arrangement shown in fig. 6 a. No trace of acetabula could be detected on any part of the superficies of these modified brachia. Each, viewed from the ventral aspect, as in fig. 6, rose out of the shallow cavity or short sheath formed by an expansion of the base of each contiguous tentacle (t, t). Of each of the tentacles a basal portion only is preserved. The dorsal division of the arm-bearing part of the head (16. fig. 5) lodged in its ventral concavity the beak with its surrounding lips, m, more definitely so located than in the female (op. cit. pl. i. fig. 5), but presenting a similar structure. The arms, 1, 2, 3, were shorter, thicker, and more obtusely terminated than in the female ; and only with a magnifying power (not |