1880.] OF THE MALE OF SPIRULA AUSTRALIS. 353 



fundibular characters of the female Spirula ('Annals,' &c., p. 4) 

 are re|)eated in the male, as, for example, the long, narrow, articular 

 cavities (Plate XXXII. fig. A, k) receiving the corresponding promi- 

 nences {ib. I) on the juxtaposed inner surface of the mantle, and the 

 small terminal valvular aperture (jn). 



The chief sexual modifications affect, as usual, the brachial part 

 of the head. 



Tlie three pairs of the ordinary arms (Plate XXXII. figs. 1 and 5, 

 1, 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') of 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, ap- 

 parently, 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 tbis 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 (i6. 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 pro- 

 portion, 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 {ib. fig. 5) 

 lodged in its ventral concavity the beak with its surrounding lips, 

 m, more definitely so located than in the female {op. cit. pi. i. fig. 5), 

 but presenting a similar structure. 



The arms, 1, 2, 3, were shorter, thicker, and more obtusely ter- 

 minated than^in the female ; and only with a magnifying power (not 



