Abstract
Heart ratios (heart weight/body weight. ×100) have been obtained for freshly killed and preserved (10% formalin) specimens of the lampreys Petromyzon marinus, Lampetra fluviatilis and L. planeri. Values for comparable stages were significantly higher in the preserved material, probably as a result of retention and fixation of blood in the heart chambers. The regression slope for the logarithmic relationship between heart and body weights was close to one in all stages of the three species investigated. A marked increase was observed in the heart ratio during metamorphosis, apparently attributable to an increase in the number and density of myocardial fibres. Heart ratios in the lamprey were generally higher than for most other fishes, with values of 0.1 and 0.3 being obtained for example in the case of freshly killed ammocoete and sexually mature adult stages of L. fluviatilis.
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