790 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



the tail. Not only so ; but the fin-membranes and the yolk-sac exhibit similar spots in 

 abundance (PI. XVI. fig. 2). They are very pale, and unless carefully looked for, readily 

 escape detection, but they are very characteristic of this fish, even in the late larval stages, 

 the pale yellow, with a distinctive greenish tinge rendering them important for diag- 

 nostic purposes. In this species one or more enucleate, elaborately stellate structures 

 frequently exist on each side of the mid-mesenteric region. Sometimes five or six of these 

 bodies appear upon the surface of the yolk near the trunk of the embryo. They have 

 the form of a " bone-corpuscle," but they are not pigmented, and their nature and meaning 

 are doubtful. In the ling, from the third to the fifth day (PI. XIX. fig. 9), while the 

 blastopore is closing, neutral-tinted amorphous spots, apparently protoplasmic aggrega- 

 tions, which send out pseudopodial processes, and thus acquire a rudely stellate form, occur 

 over the yolk-surface (vide PL XIX. fig. 9). Two days later (when about thirty 

 protovertebrse are segmented off) the trunk and fin-membranes are very richly supplied 

 with yellow pigment of a bright canary- tint (PI. V. fig. 9). This consists of unbranched 

 corpuscles, and extends also over the yolk-membrane. Black pigment likewise appears, 

 a few rude spots at first behind the eyes, and similarly it is not confined to the trunk, 

 stray stellate spots extending over the yolk-surface, and especially over the protoplasmic 

 covering of the large oily sphere (og). On the trunk, from the otocysts (au) to the tip 

 of the tail, a more or less regular linear series of stellate black spots passes, extending at 

 times over the dorsum. In M- otella, as Mr Brook (No. 31, pi. ix. figs. 7, 8a; pi. x. 

 figs. 10, 11) has shown, black pigment occurs in definite patches ; and after the embryo 

 has emerged, this definite aggregation of the spots produces a very remarkable appear- 

 ance (PI. XVII. fig. 2). 



In the few species of Pleuronectidse as yet investigated, certain common features are 

 noticeable, viz., the general occurrence of yellowish pigment (vide PI. V. fig. 6 ; PL XVI. 

 figs. 1, 3, 5, 6 ; PL XVIII. figs. 1, 2 ; PL XIX. fig. 5), and in later stages the presence 

 of two distinct colours (PL V. fig. 6; PL XVI. figs. 1, 3, 5 ; PL XVIII. figs. 1, 2). 

 On the fifth day (120th hour after fertilisation), when twenty-two to twenty-five 

 protovertebrse in the common flounder are marked off, pigment of a pale brown tint, 

 yellow by transmitted light, occurs on the sides, especially along the median lateral line. 

 Twenty hours later, black spots, very minute in size, appear, intermingled with scat- 

 tered yellow spots over the trunk and tail. The yolk, however, is devoid of pigment. 

 PL XIX. fig. 5, shows the arrangement of the yellow pigment at the time of hatching. 

 In examples at an advanced stage, e.g., twelve or fourteen days after hatching, a 

 remarkable distribution of these spots is exhibited (PL XVI. fig. 1). The brownish 

 yellow spots extend above the mid-brain (mb), around the eyes, along the mandibles, • 

 and over the abdominal region ; but are especially aggregated along the dorsum upon 

 each side of the median fin. The peculiar patches of radiate or stellate yellow spots which 

 appear midway along the embryonic caudal fin-membranes, dorsally and ventrally, will be 

 described in a subsequent page (see Median Fins). Eadiate black spots also occur 

 amongst the yellow pigment. 



