270 



Part III. — Twenty-second Annual Report 



VI. — ON THE POST-LARVAL AND EARLY YOUNG STAGES OF 

 THE WITCH (PLEURONECTES CYNOGLOSSUS, Linn.). 

 By H. CnAS. Williamson, M.A., D.Sc, Marine Laboratory, Aber- 

 deen. (Plate XVI.) 



A very complete series of post-larval and young witches has been 

 collected by Dr. Fulton and these he has handed to me for descrip- 

 tion. 



This form is especially interesting in that it has a very long post-larval 

 period ; it reaches a large size before it takes up a bottom habitat, i.e. 

 before its transformation from a bilaterally symmetrical fish to a flat-fish. 



Drawings of eight post-larval and two young stages are shown in 

 Plate XVI. An extended and detailed description is not necessary, as 

 these serve sufficiently to indicate the general form and the arrangement 

 of the black pigmentation so far as the latter has survived preservation. 

 All of the specimens had been preserved in a solution of formaline in 

 seawater. 



Cunningham* was the first to observe the larva of the witch, and 

 his description may be here incorporated. He says— " The larva is 

 not different from that of the other species of Pleuronectes ; its length is 

 3'9mm. ; there is no pigment in the eye; a number of very minute points 

 are scattered down the sides." About 48 hours after hatching, " the 



length is now increased to 5*9mm ; the median fin-fold is 



much wider ; the eye is slightly pigmented, and pigment is largely 

 developed in the skin of the body ; the cutaneous chromatophores form five 

 well-marked transverse stripes arranged in longitudinal series along the 

 sides, three of them on the tail, are in the region of the rectum, and one 

 about the pectoral fin." 



Holtf gives a more detailed account of the larva and early post-larva. 

 The additional particulars which he furnishes are the following : — The 

 larva, hatched from an egg captured in the sea, " had pigment of a pale 

 chrome colour by reflected light, and of a dark yellow by transmitted light. 

 This extended over the head, eye, and throughout the trunk and free 

 caudal region, and over the yolk .... In the next stage black 

 pigment is associated with the yellow, and also appears independently 

 along the margin of the dorsal fin. In a specimen, two days old, hatched 

 from artificially fertilized eggs the length is 5 -5mm. We now find a 

 change in the arrangement of the pigment, which is broken up into three 

 distinct bars in the post-anal region. Moreover, the yellow pigment now 

 exhibits a greenish colour by transmitted light." 



A drawing of an early post-larval stage (derived from artificially 

 fertilized eggs) ten days after hatching accompanies the following 

 description: — "The eyes are black, with a bluish lustre; the lower jaw is 

 very prominent, the pectorals very large, the otocysts large. The post-anal 

 region is very slender, especially the part ventral to the notochord ; the 

 latter is very stout. The urocyst is larger than before. A ventral patch 

 of black chromatophores has appeared midway between each post-anal 

 pigment bar. The most anterior bar, that in the region of the pectoral 

 fins, has lost its distinction. Pigment is absent from the dorsal fin in this 

 region, whilst there has taken place a considerable development of pig- 

 ment in the lower jaw and anterior ventral region ; the coloured pigment 



* Trans. Roy. Soc. Edinburgh, xxxiii., Pt. I., 1887. 

 fSc. Trans. Roy. Dublin Society (2), iv., 1893. 



