THE SEA-SCORPl ON-FAMILY. 125 



from the breast-fins to the vent. ' Pigment of a bright yellow- 

 colour by reflected, and orange by transmitted, light occurs also 

 at the base of the breast-fins, on the top of the head, and 

 on the abdominal roof.' The eyes are black with a greenish 

 iridescence. 'In the post-anal region the only pigment is a 

 ventral line of black chromatophores, sometimes very small or 

 absent in the anterior region, and ceasing before reaching the 

 tail.' 



The vitality of the larval sea-scorpions is remarkable. They 

 will survive for a fortnight in March, in a small quantity of water, 

 in a glass vessel 2 inches across and 1 inch deep. 



On the 10th October, on one occasion, a larval form 

 resembling a sea-scorpion was captured in the tow-net. In 

 general outline it resembled that figured in the 'Researches,' 

 with the vessels coursing over the yolk-sac. The oil-globule 

 remained at the anterior part of the yolk-sac. Small specks of 

 black pigment occurred along the sides of the body, one set 

 forming a row near the vipper-lateral region. No distinct 

 coloration was visible on the pectorals. The eyes were iri- 

 descent-greenish, like the inner surface of the shell of Haliotis. 



Hitherto it has been unusual to get larvae at this season 

 of the year, so that the deposition of such eggs must have been 

 antedated by some months on this occasion — if the inter- 

 pretation of the nature of the larvae be correct. 



Swarms of the early post-larval sea-scorpions, indeed, just 

 after the absorption of the yolk, about 1 to 7 '.5 mm. (in spirit), 

 are occasionally captured in the surface tow-nets, as in the 

 Forth, e.g. in March and April. Such pelagic forms have only 

 embryonic rays in the tail-fin. The body and tail are trans- 

 lucent, whilst the head and abdomen have a pale greenish hue 

 with black chromatophores, and the eyes have a silvery lustre. 

 A line of black pigment-specks runs along the ventral edge of 

 the muscle-plates behind the vent almost to the tail. 



Mr Holt' observed that the lower jaw is movable two days 

 after hatching, and that the vent is open. In our examples, a 

 thickening below the axis of the tail occurred. When six days 



1 E. W. L. Holt, Sc. Trans. Roy. Dab. Soc, v. 2, p. 21, &c. 



