Develo])ment of the Food-Fishes. 459 



(2) The Embryos. — There is little doubt that the pigmenta- 

 tion of embryonic Teleosteans is a feature of great diagnostic 

 value. The valuable observations of Agassiz"^ upon this 

 subject are well known ; but with the exception of Professor 

 M'Intosh's contributions on the subject very little has been 

 done. The study of an extended series of embryos o,lone can 

 establish the validity of pigmentation as a means of identifica- 

 tion ; but observations at the St. Andrews Laboratory lend 

 considerable countenance to the contention that embryonic 

 coloration is diagnostic. 



Pigment appears in P. jlesus at the earliest stage, and is, as 

 Prof. M'Intosh describes f, " of a peculiar pale olive-brown 

 (brownish yellow by transmitted light)," forming distinct 

 patches on the dorsum and tail, with intervening lines of 

 spots. Pigment of a more distinctive yellow colour — a rich 

 amber shade — appears in P. limanda. Its distribution is 

 similar to that in P. flesus ; but in neither species does it 

 extend over the yolk. Large stellate black pigment spots 

 occur in the more advanced embryos of P. limanda^ extending 

 over the eyes, otocystic and hepatic regions to the anus, and 

 along the dorsum and upper margin of the caudal trunk. 

 Crescentic yellow pigment patches appear in the caudal mem- 

 brane. 



G. merlangus exhibits no coloration until the eighth day 

 after hatching, when pale yellow amorphous corpuscles appear, 

 chiefly on the dorsal and lateral surfaces; they extend also 

 over the yolk-surface and embryonic fin-membrane. The 

 tint is characteristic — a pale yellow with a distinctive gi-een 

 tinge. In the two remaining Gadoids black pigment alone 

 appears — in Gadus morrhua two days before emerging from 

 the ovum, and in G. ceglejinus on the eleventh day, in a series 

 which emerged on the twentieth day. In both the spots are 

 at first amorphous and confined to the dorsal aspect of the 

 trunk ; but they rapidly extend, especially in the ventral or 

 mesenteric region and region of the shoulder, the pectoral 

 fins being also radially pigmented. T. gurnardus is scantily 

 pigmented on the eleventh day, the spots being of a pale sea- 

 green hue ; but two days later yellow corpuscles are plentiful, 

 and a few are of an ochrcous hue. Lastly minute black spots 

 occur. The surface of the yolk becomes rapidly pigmented 

 as well as the proto})lasmic investment of the oil-globule. It 

 is well known that monsters frequently occur : but these were 

 rare in the large number of embryos reared at St. Andi-ews. 



* Proc, Amer. Acad. Arts and Sci., June 1878, pp. 1-18. 

 t ' Second Annual Report of Fishery Board for Scotland,' 1884, Ap- 

 pendix F, p. 47. 



