THE GROWTH OF CERATIAS HOLBOLLI 15 



I believe that this is good evidence that all the thirteen specimens considered belong to a single 

 species, and that the differences between measurements for any particular dimension may be attributed 

 to simple allometry. 



These graphs, therefore, provide a fairly complete picture of relative growth in Ceratias holbolli 

 Kroyer from i-6o to 68 cm. standard length, i.e. from juvenile to adult size. Accordingly, for each 

 dimension the growth constant (a) has been measured ( = tangent of the angle of slope of the straight 

 line). Table 2 shows these growth constants. 



It will be seen that in twelve of the dimensions (c, e, f, g, h, k, m, n, o, q, r, s) growth is isometric, 

 i.e. a= 1 ±0-05. This group includes the dimensions relating to the positions of the dorsal and anal fins 

 which Parr found to show small differences in his two specimens of Mancalias uranoscopus (Table 1 , nos. 3 

 and 10). In the run of specimens now being examined the small differences are found not to be significant. 



Regarding the same two specimens Parr also found that the following dimensions were relatively 

 smaller in his larger specimen (no. 10) : length of maxillary, length of lower jaw and depth of caudal 

 peduncle. This is substantiated in Table 2, where these three dimensions (/, j and /) all show slight 

 negative allometry (a = 0-90 — 0-92). The distance of the base of the tentacle (papilla, pore) on the back, 

 to the dorsal fin (p), is likewise slightly negatively allometric (a = o-g2). Parr's observation was the 

 converse of this, a discrepancy due, as he suspected, to the damaged condition of his larger specimen. 



The length of the illicium (a) shows marked negative allometry (a = 078). Bertelsen also drew 

 attention to the decrease in length of the illicium and the jaws with increasing length of the individuals. 

 Since the total length of the basal bone (c) remains isometric, it is likely that the pronounced decrease in 

 the relative length of the illicium during ontogeny is associated with the negative allometry of the jaws 

 (z andy), and perhaps with an increase in the distance that the basal bone can be retracted. The relative 

 growth of the illicium would then be such as to keep the esca in line with a bisection of the angle 

 of gape when the lure is retracted. 



It will be seen that in Ceratias holbolli there is considerable reduction in two of the sense organs 

 during growth to adult size. Data on the diameter of the eye (t) and the length of the nostril (u) are 

 confined to the four specimens (nos. 1, 5, 9 and 12) which I have myself been able to examine. The 

 points plotted on the log log scale are grouped sufficiently close to a straight line to advance values for 

 the growth constants of about o-6 for the diameter of the eye and 0-8 for the length of the nostril. It 

 is significant that in C. holbolli the eye should show the greatest degree of allometry among the organs or 

 dimensions investigated. It may be recalled that both the Antarctic specimen and Regan's specimen 

 (nos. 9 and 12) are functionally blind. Now, in the two other specimens I have examined, viz. the 

 second specimen of Mancalias bifilis Regan & Trewavas and the type of Mancalias tentaculatns Norman 

 (nos. 1 and 5) which may now be regarded as juvenile Ceratias holbolli, the eyes, although reduced, are 

 exposed and doubtless functional (Fig. lb). It is clear therefore that the eyes, besides suffering re- 

 duction during ontogeny become also subcutaneous and acquire the condition of the eyes of the adult 

 forms (nos. 9 and 12). A transparent disk, surrounded by a pigmented ring, has been mentioned lying 

 just ventral to the concealed eye in the Antarctic specimen. This structure represents the conjunctiva 

 of the eye in the juvenile fish, and the subcutaneous condition would have been achieved by the 

 establishment of an active growth centre, at some stage in ontogeny, in the skin immediately above the 

 eye. Such locally accelerated skin growth would then carry the conjunctiva and its pigmented border 

 bodily across the eye and so conceal it. Even in the stage represented by ' Mancalias bifilis ' (no. 1) the 

 shape of the aperture of the eye suggests that the occluding process may already have begun (Fig. iB). 

 The final condition would be that found in the Antarctic specimen (Fig. 1 A). The fact that Gaimard's 

 figure of the type specimen shows visible eyes does not by itself invalidate the argument. Their portrayal 

 may be accountable to the artist, or to some damage of the material which revealed the eyes. 



