90 On Oleaginous Spheres hi the Yolk of Teleostean Ova. 



developmental conditions. May not this fact throw light upon 

 the significance of these globules ? We have seen that their 

 presence cannot be explained by resorting to a hydrostatic 

 function, and there are great difficulties in the way of the 

 nutritive theory. Is it not possible that they may have some 

 ancestral significance ? The distinctive coloration they ex- 

 hibit is an interesting point, though it can give no aid in the 

 matter. Nevertheless it is remarkable that the orange tint 

 of these spheres, in the ovum of the Salmonoids, is precisely 

 that which distinguishes the oily matter in the muscular 

 tissue of the adult fish. The flesh of the common mackerel, 

 the Spanish mackerel, and the gurnard, not to mention others, 

 is regarded as somewhat oily, and the ovum of each of these 

 fishes exhibits a large globule. The oleaginous matter in the 

 flesh of the last-named fish is of the same tint as that of the 

 sphere in the ovum. The globule in the ling is of a pale 

 green hue; and in the allied form, the burbot, Van Bambeke 

 describes it as " tr^s-r(jfringente, d'une teinte jaunatre "■^. 

 The globules in the fifteen-spincd stickleback, and in certain 

 Cottoids, are of an amber colour, but in many forms (e. g. Cijclo- 

 2yterus, CoUus, Motella, &c.) they are almost perfectly colourless. 

 These features are of minor importance, however, compared 

 with the fact that in the ova of so many species of Teleosteans 

 large spheres of a substance closely connected with the lecithin- 

 group should occur. Lecithin is peculiarly active in all 

 embryonic development, and the possibility is suggested that, 

 though the matter constituting these globules may be dispro- 

 portionately large as compared with the volume of the vitel- 

 line mass, yet it was not always so. That the yolk-matter 

 of the Teleostean ovum was once greater in bulk than it is 

 now, is (in accordance with Balfour's viewf) an accepted con- 

 clusion. If as the vitelline mass diminished the lecithin or 

 similar fluid did not decrease in the same degree, globules 

 would be formed precisely as we find them in so many Tele- 

 ostean eggs. The amount is more than the necessities of 

 development appear to require ; and thus we find that during 

 the growth of the blastoderm, and during the early stages 

 of the embryo, these superfluous elements are not utilized and 

 do not ajjpreciably decrease in volume. They are enveloped 

 by the blastoderm, and in the liberated embryo generally 

 occupy a posterior position in the diminishing yolk, on the 

 ventral surface of the young fish. Finally they disappear in 

 the last stages of larval life by absorption ; but up to that 

 point retain the character of redundant and superfluous ele- 

 ments in the deutoplasmic mass. 

 * Loc. cit. p. 5. t Jc'uni. Anat, and I'liys. vol. x. p. 5-51. 



