VASCULAR SYSTEM OF IISIIES. 253 



' precaval ' trunk. A corresponding precaval trunk is formed in the 

 same way on the left side, and the great auricular sinus is con- 

 stituted by these and by the wide hepatic veins, which contract before 

 they terminate. In many Osseous Fishes, as Salmo, Silarus, Belone, 

 Angiiilla, Ammodytes, and Accipenser, the hepatic veins terminate in 

 the common sinus by a single trunk ; in others, as Thynnus, Gadus, 

 Esox, and Pleuronectes, by two trunks; and in a few Fishes, as 

 Clupea, Cottus, and certain Cyprinoids, by three or more trunks. 



Thus in Fishes the chyle, liaving already begun to manifest its 

 independent life by the development of distinct microscopic granular 

 corpuscles, as primitive centres of assimilative force, before it enters 

 the lacteals, undergoes in those vessels and their receptacles a fur- 

 ther stage of conversion into blood by the reaction and, as it were, 

 impregnation of the lymph, and by the interchange of properties 

 therewith : the vitalising stimulus of which interchange and reaction 

 is manifested by the repeated spontaneous fission of the corpuscles, 

 many of which now acquire a capsule, and thus become nuclei of 

 cells. Then the mixed chyle and chyme enter the veins, where a 

 further interchange of properties with the venous blood and a new 

 course of action and reaction take place. The primitive pale chyle- 

 corpuscles are here few in number ; they have a capsule, and the 

 granular character of their contents shows them to be in the course of 

 change : a centre of superior assimilating force has already begun to 

 establish itself amongst them, and to grow at their expense. * 



THE IIEAltT. 



The venous blood undergoes some change, probably, in its passage 

 through the kidneys, by virtue of the anastomoses of the renal vascular 

 system : it undergoes further cliange in its circulation through the 

 liver, in so far as the bile, a fluid highly charged with carbon and 

 hydrogen, is eliminated from it : it is said that in some fislies 

 (^Myx'me, BdeUostomd) a contractile receptacle accelerates its course 

 through the portal circulation. The venous blood has finally to be 

 submitted to the influence of the atmosphere, and especially to the 



* IMost of the stages analogous to tliose ilcmonstratcd by Dr. INIartin l?arrv 

 (cvii.), in the first periods of development of the niammiferoiis ovum, liave been 

 recognised in the corpuscles of chyle, lynipli, and blood. The powers of one series 

 of granules, the progeny of a primary centre, are concentrated in a secondary 

 nucleus, which absorbs them as they liquefy ; developes itself at their expense, 

 generates a second series of granules, which, in their turn, give way to subserve a 

 third regeneration of aggregated but distinct spherular centres of force ; the final 

 purpose of the successive development, liquefaction, and assimilation of the inde- 

 pendent granular centres, being apparently to concentrate their vital energy in the 

 form idtimatcly assumed, as coloured blood-discs. The shapj and relative si/e 

 of these particles are shown m fig. 4. p. i;j,in a plagiostomous fish at /t, in a typical 

 osseous fish at </ ; the blood-discs of the Lamprey arc circular. — See the admirable 

 Memoir on the Development of Ulood-discs. cxxvii. 



