VEINS OF FISHES. 469 



checquered more or less with stellate pigment ; in shape fusiform, 

 fig. 309, A, or pyriform, ib. b ; at the distal end it is connected 

 with a small vein, c, which collects the blood from the capillaries 

 of the tail, d, d' : at its proximal end it is connected with the 

 commencement of the cardinal vein, b. The blood, which is deep 

 red, appears to flow into the sac in a continuous stream from c ; it 

 is forced out at each contraction in an interrupted current, quickly, 

 in successive portions, into b, where the movement soon subsides 

 into a continuous stream. During the systole the veins c and b 

 are lengthened, being drawn out ; in the diastole they resume 

 their size, and assist in elongating the sac ; which, both by 

 its contents and connections, is to be regarded as a e venous 

 heart.' l 



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

 independent life by the developement of distinct microscopic 

 granular corpuscles, as primitive centres of assimilative force, 

 before it enters the lacteals, undergoes in those vessels and their 

 receptacles a further 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 inter- 

 change 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 

 takes 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. 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 change in its circulation through 

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

 carbon and hydrogen, is eliminated from it : that in some fishes 

 (Myxine, Bdellostoma) a contractile receptacle accelerates its 

 course through the portal circulation. The venous blood now 

 shows a marked accession of coloured corpuscles ; and it has 

 finally to be submitted to the influence of the atmosphere, and 

 especially to the reaction of the oxygenous element ; and for this, 

 the most important and efficient cause of its conversion into 

 arterial blood, a contractile cavity, Avith strong muscular walls, is 

 provided, in order to impel the blood to the organs especially des- 

 tined to effect its decarbonisation and oxygenation. 



1 cxlv. p. 253 (1840). 



