l'I.All'ISIll-;S (HI-.I1CI«)S(_).MA'1A) 



y. i)h\i:i.()pmi-:nt. 



The \aiious stages in the development of a nnnibcr of Flattishes liave now been 

 slii<lie<l in detail, especially of those species which are valued as food. References to 

 the more important papers describing the eggs, larvae and young are given in the 

 systematic part of this work under the inilividual species. The main features of 

 Klathsh development are too well known to require description at length, but one 

 or two points, which are of interest in connection with problems of taxonomy or 

 geogra])hical distribution, may be briefly considered.^ 



The eggs of the great majority^ of the Flatfishes are buoyant and pelagic, the only 

 exception among those which have been studied being Pseudopleiironectes aiiiericanus, 

 of which the eggs are .said to be demersal and adhesive. Those of Solca have a number 

 of small oil-globules at the surface of the yolk, but in all the members of tlie families 

 Bothidae and Pleuronectidae the oil-globule is either single or absent altogether (Fig. 

 .;o). It IS of some interest that, in addition to the monomorphic optic chiasma 

 mentioned in the previous section, the sinistral Bothida? are well distinguished from 

 the dextral Pleuronect^da^ by the form of the eggs.- Those of Paraltchthys, Eucilliarus, 

 Antoglossiis, Boihus, Scophthahnns, Lepidorhombtis, Phrynorhombus and Zeiigopterus 

 have a single oil-globule in the yolk ; those of Hippoglossiis, Hippoglossoides, Limanda. 

 Murostoinus, Glyptocephahis, Platichthys and Plciironcctfs have an undivided yolk 

 without an oil-globule.^ 



In most respects the early larv;e of the Flatfishes are very similar to those of 

 ordinary symmetrical fishes, and it is only as the time for the metamorphosis approaches 

 that they assume the specialised features characteristic of the group. The post-larval 

 characters may be roughly divided into two categories, permanent and temporary. 

 The former includes the migration of the eye, growth of the pelvic and caudal fins, 

 enclosure of the abdomen, etc., and need not be considered further. The second 

 category includes purely temporary organs which are developed during post-larval 

 life and disappear when the transformation is complete or even before. These are 

 the air-bladder, post-larval teeth, dorsal tentacles, spines, pigmentation and so on. 

 In a genus such as Aytioglossus, where these temporary post-larval characters are more 

 remarkable and diverse than in any other genus of Flatfishes, a full knowledge of 

 these characters may be of considerable assistance in elucidating the taxonomy of the 

 group, a fact which is well brought out by a study of Kyle's work on the European 

 species. 



One of the most characteristic temporary characters of the post-larval Arnoglossus 

 is the long appendage or tentacle on the head (Fig. zi.\). This appears quite suddenly, 

 according to Kyle, as the result of a longitudinal splitting of the upper margin of the 

 embryonic dorsal fin in the region of the second ray of that fin ; it appears long before 

 the fin-rays are developed and disappears with equal rapidity during the period of 

 tlie migration of the eye. This appendage is not peculiar to Arnoglossus, but is also 

 present during the early stages in Bothtis, in which genus, however, it disappears at 

 a very early stage of piost-larval development (Fig. 21B). It probably also occurs 

 in other related genera from tropical and temperate seas. Kyle (1913, p. 39) regards 

 the tentacle as a means of guarding against damage to the anterior part of the cranium, 

 which at this stage is <)uite unprotected. In the post-larval Symphnms (Cynoglossida?) 

 the first three rays of the dorsal fin are somewhat prolonged, this number being later 

 increased to five. 



\ lertain number of species of sinistral Flatfishes (Bothidae) develop spines in one 

 form or another during the post-larval stages. In Arnoglossus there is a well-developed 



' lur iii.itiy of the facts coiici.TmnK l.irv.il and po5t-larv.il l-l.illishi-s tlic author i5 mdi-bted to 

 .1 valuahic paper by Kyle (191,;). 



2 Rcf^an (1910U, p. 489). 



■' In Psciulo!>leuroncctcsanuruanus the c-g-. when hi^l f.Mrudfrl, ha^ Jio oil-globulc, hut in 

 liio*t pgss one li dcviloped at .1 l.itii ^taRi 



