DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 781 



the stronger and more robust Teleosteans, which are at a very early stage, often long before 

 extrusion from the egg, provided with a complex vitelline circulation. In such forms as 

 Salmo (PI. XXII. figs. 4-9), Anarrhichas (PL XX. figs. 2, 4, 5), Gastrosteus, Cottus, 

 Liparis (PI. XV. fig. 2), and Cyclopterus, the blood-corpuscles seem to be mainly 

 derived from the nucleated particles into which the surface of the yolk becomes broken 

 up, and, as already noted, Truman found in Esox that haemal channels appeared upon 

 the yolk, and corpuscles slowly moved towards the heart before this organ showed any 

 motion. No such blood-canals are excavated in the yolk of the pelagic forms here 

 treated of, indeed no yolk-circulation ever truly exists in the gurnard, cod, and allied 

 forms. Nevertheless, the yolk steadily diminishes, and in embryos, fourteen to twenty 

 days after hatching, it forms but a very slight projection, and at the end of the first 

 month would appear to be entirely absorbed (compare fig. 5, PL XIX. and fig. 1, 

 PL XVI.). The surface of the yolk, however, shows during this time rapid disintegration 

 [vide PL VII. fig. 9), vesicles, granules, and nucleated particles appear in it (PL XI. 

 fig. 12), and are especially noticeable around the large oleaginous spheres (PL XL 

 fig. 13) in those forms, such as the gurnard, ling, and others, in which these striking 

 bodies occur. The protoplasmic envelope of the globule in such cases becomes richly 

 provided with large nuclei showing one or more nucleoli, and similar bodies occur 

 superficially over the yolk. In a young perch, eleven to fourteen days old, Lereboullet 

 observed, just as we have noticed in the Gadoids and other forms, the dorsal aorta, formed 

 by the union of the vessels of the branchial arches, sending a supply to the intestine and 

 adjacent viscera, and reaching to the extremity of the tail, while of venous trunks the 

 two anterior and two posterior cardinals and the subintestinal vein are common to both. 

 In Perca, in addition to the above trunks — developed no doubt in all Teleostean larva?, 

 a complex yolk-circulation arises, and is supplied by branches from the posterior cardinals 

 and from the subintestinal vein. These branches pass over the yolk as simple undulating 

 lacunae formed by the separation of the substance of the yolk-cortex, and meet on the 

 ventral side of the yolk in a pair of large veins, which form one large sinus, continuous 

 with the sinus venosus in the pericardial chamber. Lereboullet says of these vitelline 

 vessels, that they do not appear to have proper walls, and form an ill-defined and irregular 

 network; but on the third or fourth day after hatching the haemal canals acquire definite 

 walls, the network elongates, so that the main trunks show a parallel arrangement (No. 93, 

 p. 601). In Perca the development of this circulation over the yolk is much more rapid 

 than in Esox, and Lereboullet connects this with the larger perivitelline space in Perca, 

 as there is a greater need for respiration; and for this reason, he says, in that species " the 

 capsule is spacious, and holds so large a quantity of water" (No. 93, p. 610). The true 

 explanation, however, seems to be that the more complex and rapid the circulation the 

 more speedily the bulk of the yolk is reduced, and hence a large perivitelline space is 

 produced. It is remarkable, however, that in such forms as the gurnard, rockling, the 

 flat fishes, and Gadoids, in which no vitelline circulation ever develops, the yolk should 

 still show a very rapid disintegration (compare PL XII. figs. 1 and 3, with PL X. 



