22 REPEODUCTION AND DEVELOPMENT OF TELEOSTEAN FISHES 



But I am able to confirm entirely Mcintosh's statement with 

 regard to G. lyra. I examined ripe ova squeezed from a mature 

 female, and saw the hexagonal reticulum figured by Mcintosh, and 

 further, I took in the tow-net in the Firth of Clyde in 1886 an ovum 

 well advanced in development, which showed exactly the same 

 marking, and which agreed in all characters with the ripe ovum of 

 0. lyra. Moreover, I saw no layer of yolk-segments in this species. 

 At Plymouth I again met with the same ovum on February 1st, 

 1888, inside the Sound ; two views of it are shown in figs. 26 and 27 ; 

 the former shows an optical section, the latter the surface of the 

 vitelline membrane. This ovum measured in one case "90 mm., in 

 another '97 mm. Raffaele gives as the diaineter of the ovum of 

 G. festivus "56 to '60 mm. The Italian author speaks as if he had 

 taken the ova directly from the parent fish, and thus it would seem 

 that there are great differences between the ova of these two species 

 of the same genus, but they agree in having no oil-globules. 



The other kind of ovum with a peripheral layer of yolk-segments 

 is briefly described by Raffaele (No. 2 of his undentified species) . 

 This has a diameter of '75 mm., and has a number of rather large 

 oil-globules scattered separately over the yolk ; it was obtained by 

 the tow-net in January. 



As it seems not quite certain that the identification of the ovum 

 of Temnodon by Agassiz and Whitman is correct, and there is some 

 doubt about Gallionymus festivus and the other species, Mullus and 

 Solea are left as the only genera whose ova undoubtedly have the 

 peripheral layer of yolk-segments. It is interesting to notice that 

 these ova present a condition of the yolk intermediate between that 

 characteristic of non-pelagic ova and that seen in typical pelagic 

 ova. Oil-globules occur equally, either singly or in numbers, in 

 both kinds of ova, but in all adhesive ova the yolk is made up of a 

 number of minute yolk- spheres, and in nearly all pelagic ova 

 the yolk is one mass, continuous and homogeneous, a single yolk- 

 sphere. The adhesive ova are characteristic of nearly all shore 

 fishes from the large Cyclopterus to the minute Goby, and also of 

 the greater number of Physostomi, i. e. of the more primitive fishes 

 with an opening to the air-bladder. But certain Clupeoids, e. g. 

 the pilchard, although belonging to the Physostomi, have pelagic ova, 

 and in these ova the subdivision of the yolk is retained at all stages ; 

 then in Solea and Mullus the central part of the yolk is fused into 

 one mass, while a peripheral layer continues segmented ; and finally 

 in most pelagic ova the segments disappear altogether, and there is 

 no subdivision of the yolk at all. It is possible that the peculiar 

 character of the ovum of Solea indicates that there is no close 

 affinity between this genus and Pleuronectes ; the adaptation to the 



