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



sparsely in linear areas along the summit of the head, the opercular region, and on the 

 snout. In form the spots are amorphous or rudely stellate. Along the huge pectoral fins 

 and the ventrals similar minute corpuscles are developed, mingled in the former pair of 

 fins with yellow pigment-spots (PL XVII. fig. 5). 



Certain features in the development of the pigment are noticeable, such as the fact that 

 in some Gadoids the spots are confined solely to the trunk (cod, haddock, and rockling), 

 (vide PL XVII. figs. 1,2); while in the whiting (PL XVI. fig. 2), the sole and the ling 

 (PL V. fig. 9), the covering of the yolk (y) becomes richly pigmented. This pigmenta- 

 tion of the yolk-sac is a feature also in the gurnard (PL XVI. fig. 8), and in the latter and 

 the ling coloration is preceded by the appearance of colourless corpuscles, which are 

 scattered over the yolk-sac {vide PL XIX. fig. 9). Pale neutral tinted bodies, evidently 

 protoplasmic, and of various angular shapes, are distributed over the yolk-surface. They 

 send out pseudopodia, and become rudety stellate, In the ling this occurs on the fifth 

 day after fertilisation — about the time that the blastopore closes ; and in the gurnard at 

 a similar stage these protoplasmic particles with short processes also appear. These 

 bodies are obviously only a cortical disposition of protoplasm — less delicate and complex 

 than the elaborate network of protoplasmic threads which extends over the yolk-sac in 

 the cod, haddock, flounder (PI. XIX. fig. 5), dab (PL V. fig. 3), and other forms. 



The pigment-spots which occur over the yolk-surface are beneath the cellular germ- 

 layer. They develop, as Ryder has pointed out, in the non-cellular periblast ; and Cun- 

 ningham, while noting this condition, viz., that " they are situated at the surface of the 

 periblast," in Pleuronectes microcephalics and Scomber, states that in the latter species the 

 pigment is confined to the deep surface of the oil-globule and the sides of the embryo. 



If the large multipolar corpuscles in the ling and gurnard be merely the nodes or 

 thickened points of intersection for the protoplasmic threads crossing over the whole yolk- 

 surface, it is remarkable that these points of intersection should not develop pigment in 

 the cod and dab, whereas they apparently become the pigment-spots of the yolk-sac in 

 the ling and gurnard. The actual transformation of the colourless corpuscles into 

 pigment-spots was not observed, but it is very probable.* 



The pigment-spots of the embryonic trunk often form distinct papilliform projections, 

 the growth of the corpuscle pushing the epiblast out, and forming a small mound at that 

 point. If the development of a pigment-spot be followed in the ling or gurnard (vide PL 

 V. fig. 2), we see a rounded or irregular particle of clear protoplasm superficially placed 

 upon the yolk-surface, which shows amoeboid movements, and sends out blunt processes 

 (PL I. figs. 8a, 86). These processes become bifurcate, and assume a more or less elabo- 

 rate ramose disposition — a stellate corpuscle being the result (PL V. fig. 2b). In the 



* In Gastrosteus Kupffer speaks of the appearance on the yolk-surface of small nuclear bodies, from which he says 

 not only pigment, but blood-corpuscles are formed. These nuclei, probably the nuclear bodies already referred to in 

 the allied marine species (p. 55), which become radiate in form, develop pigment-particles, the others keep their 

 original shape until they are set in motion by the establishment of a blood-circulation (No. 88, 1868). In Gastrosteus 

 spinnr.hia, the yolk-cortex, even before the blastopore closes, presents a striking appearance on account of the large 

 translucent nuclei which are scattered all over it. These nuclei often show many nucleoli (vide No. 124, p. 493), and 

 in the freshwater species, G. aculeatus, a reticulation is also present, but this has not been observed in G. spinachia. 



