A treatise on zoology . [168], Cori [93], Julin, Dohrn). Soon thislatter vein breaks up in the liver into the hepatic portal capillarysystem, its anterior portion forming the hepatic veins. Theinferior jugulars are replaced by a median inferior jugular belowthe ventral aorta. This vein, and a ventral hepatic vein, arepeculiar to the Cyclostomes (Fig. 18). The two anterior and alsothe posterior cardinals join above the oesophagus to large trunks,which open to the right into the dorsal limb of the sinus ductus Cuvieri on the left side thus disappears, and all thevenous blood pours in
A treatise on zoology . [168], Cori [93], Julin, Dohrn). Soon thislatter vein breaks up in the liver into the hepatic portal capillarysystem, its anterior portion forming the hepatic veins. Theinferior jugulars are replaced by a median inferior jugular belowthe ventral aorta. This vein, and a ventral hepatic vein, arepeculiar to the Cyclostomes (Fig. 18). The two anterior and alsothe posterior cardinals join above the oesophagus to large trunks,which open to the right into the dorsal limb of the sinus ductus Cuvieri on the left side thus disappears, and all thevenous blood pours into the heart on the right side. In theMyxinoidea, strangely enough, it is the left ductus which persists,and the right ductus which is suppressed (Figs. 32, 34). The pronephros nearly disappears in the adult Lamprey, butpersists as an organ of considerable size in Myxinoids (Fig. 27).It is, however, degenerate (Weldon [483], Semon [400], Kirkaldy[263a]), consisting of a few branching tubules, o— le one 44 CYCLOSTOMATA. = o o w - - llllll ^?gj I S.| is g _ o _ ly X C 9-c ^ 5 - T ? 5: = = g ^ 3 t- ^ S tj OS c ^ ~ ?—2 ^ C3 ^ .-— ?3 5 £ --£.2 «x ?- r, = c 5 GONADS 45 hand into the pericaidial coeloni, and on tlic other into discontinuousremains of a longitudinal duct lying in a venous sinus. There is nocommunication with tlie kidne}^ duct. Degenerate as this organ is,it is better developed in the Cyclostomes than in any known adultCraniate, excepting perhaps some aberrant Teleostei (p. 364). The permanent functional kidney, or mesonephros, is repre-sented by a single longitudinal duct on each side, into which opena number of tubules leading from closed renal capsules withglomeruli (Fig. 32). In all cases the tubules have lost their pi-imi-tive openings into the abdominal coelom ; in Petnmvizon they do
Size: 1043px × 2396px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
