1894.] TELEOSTEAN MORPHOLOGY. 435 



in specimens exhibiting the Cyclopean malformation: behind a 

 line drawn through the preopercular keel the blind side may be 

 almost entirely coloured in Turbot which are otherwise perfectly 

 nornial \ Now the Cyclopean condition may be described as the 

 failure of the anterior part of the dorsal fin, and of the intenieural 

 bones and muscles belonging to it, to become united to the top of 

 the head, accompanied with a partial, if sometiuies very slight, 

 arrest of the normal transit of the upper eye. No one has had an 

 opportunity of watching the development of a Flat-fish so deformed, 

 but the variability in the different phases of metamoi-phosis which 

 one notices in looking over a collection of partly symmetrical 

 larvae suggests a more or less plausible explanation of the mere 

 mechanical process. Each part appears, as it were, to change 

 independently, so that, assuming a slight want of hai'mony in the 

 movement of the upper eye and the forward extension of the 

 dorsal (whether by retardation of the first or acceleration of the 

 last), it is conceivable that a condition might arise in which the 

 eye would obstruct the progress of the dorsal, and so compel its 

 anterior extremity to project instead of proceeding as usual along 

 the top of the head. Since the dorsal wall of the upper orbit is 

 formed in normal specimens (of the Turbot) by the base of the 

 dorsal, the failure of the latter to advance in the normal manner 

 would leave the eye devoid of its usual support, so that it would 

 rest, as it actually does in Cyclopean specimens, against the ridge 

 of the sliull, and so be more dorsally and less laterally directed 

 than in normal examples. 



The authors referred to arrive at no conclusion as to why 

 Cyclopean examples should be ambicolo.ate, but (p. 808) reject 

 Giard's theory that young fish so affected remain pelagic for a 

 longer time than usual, and so expose the blind side longer to the 

 light, whereby it retains its pigmentation instead of becoming 

 colourless. In this I am inclined to agree with them, but since 

 we know from Mr. Cunningham's own observations that metamor- 

 phosing Flat-fish, if pelagic, swim in such a position as to keep 

 both eyes in one horizontal plane ^, it would seem to follow that 

 in young Cyclopean examples, the period of pelagic life being the 

 same, the change in position is never carried to quite the same 

 extent as in the case of normal larvse. Hence the side normally 

 colourless in the adult would be a little more exposed to the light, 

 without any elongation of the pelagic period. It can hardly be 

 contended, however, that a difference so comparatively trifling is 

 sufficient to account for so marked a discrepancy in the coloration 

 of all Cyclopean and most normal Turbot. 



Another abnormality, exemplified by a Turbot and a BriU in my 

 possession, is referred to by Messrs. Cunningham and McMunn 

 (p. 807), from a description of the Brill, at that time living in the 

 Cleethorpes aquarium, communicated by myself. In these speci- 

 mens the eyes are normal, but a short portion of the anterior end 



^ See postscript, p. 446. 



2 Nat. Science, vol. i. March 1892, 



