444 Holt — On the Eggs and Larvce of Tcleosteans. 



Another egg of this species, which on the 30th June contained an advanced 

 and pigmented larva, was found twenty-four hours later to have hatched. 

 The larva (fig. 42) is probably now at least twelve hours old, and shows a 

 considerable advance on the newly-hatched condition. The total length is 

 2"20mm., having increased by •12 mm. The yolk is much reduced, and has now 

 an elongated ovoidal shape, narro-west in front. The fore brain has undergone a 

 certain upward rotation and the pineal {pn.) is visible as a distinct prominence in 

 profile. No mouth is as yet present, but the development of a pre-nasal rostrum has 

 increased the acuteness of the frontal angle, imparting to the head something of 

 the shovel-like contour familiar in the adult. The hind brain is shortened, 

 bringing the otocysts [ot.) nearer to the eye. There is as yet no appearance of 

 the enormous development of the brain met with in older stages,* and the eye is 

 still comparatively large. The pectorals [p-f.) have appeared as small semicircular 

 flaps in rear of the otocysts. Beneath them the gut shows a dilatation. The pos- 

 terior region of the gut now extends some way behind the yolk under the noto- 

 chord, the cord-like rectum (r.) descending to the marginal imperforate anus {a.) 

 at a short distance behind the yolk (//.), a condition due to the shortening up, by 

 absorption, of the latter. The post-anal region measures 1'18 mm., the anus being 

 slightly anterior to median. 



The marginal fins have undergone considerable expansion, especially the dorsal, 

 which now commences at the snout, passing up over the fore- and mid-brain as a 

 narrow fold, and thence increasing till it reaches its greatest height above the 

 posterior extremity of the yolk. The embryonic caudal fin is not affected by this 

 expansion, but embryonic fin rays have appeared in it (fig. 42). 



The arrangement of the pigment has undergone certain changes. The chro- 

 matophores over the posterior two-thirds of the yolk sac have become stellate. 

 Pigment has appeared round the inner edge of the iris. The body pigment is 

 now restricted to the neighbourhood of the otocysts, the post-anal band (p-b.), 

 which is more conspicuous, and the caudal extremity, where the chromatophores 

 are now aggregated into a dorsal and ventral patch. The two lateral lines of 

 chromatophores in the anterior region have disappeared, or have in part migrated 

 to the posterior extremity of the tubular part of the gut, and the narrow rectal 

 region. One chromatophore occurs on the pectoral fin. 



The two marginal patches of the dorsal fin have increased in size, but have 

 migrated backwards, and now occupy the extremities of tlie central third of the 

 expanded portion of the fin (i. e. the part between the mid-brain and caudal fin). 

 A large marginal patch has appeared on the ventral fin below the post-anal bar, and 

 small chromatophores occur along the edge of the fin from this point to the 



* Cf. M'lutosh and Prince, oj). cit., p. 864. 



