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THE FORM AND FUNCTION OF THE FORE‐GUT IN ANURAN LARVAE (AMPHIBIA, SALIENTIA) WITH PARTICULAR REFERENCE TO THE MANICOTTO GLANDULARE
Author(s) -
GRIFFITHS I.
Publication year - 1961
Publication title -
proceedings of the zoological society of london
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.915
H-Index - 96
eISSN - 1469-7998
pISSN - 0370-2774
DOI - 10.1111/j.1469-7998.1961.tb05901.x
Subject(s) - larva , function (biology) , form and function , biology , zoology , ecology , evolutionary biology
The structure and development of the larval fore‐gut is described in Rana ridibunda. It is shown that the manicotto is formed from elements of the ventral pancreatic anlage which proliferate within the limits of the gut‐wall. The pattern of the manicotto is examined in seventy‐five anuran species representing thirty genera and nine families. Three main deviations from the typically ranid plan are described: ( a ) persistence of a manicotto / pancreatic bridge until late metamorphosis (e.g. in Heleophryne rosei ); ( b ) restriction of manicotto tissue to the pancreatic half of the gut tube ( Alytes obstetricans ) and ( c ) concentration of the gland into a discrete, muscular fore‐gut diverticulum ( Philautus gryllus ). In ( b ) and ( c ) specialized mechanisms for sorting gut contents are also described. Defined regions of the fore‐gut are examined for enzyme action. It is shown that the manicotto functions proteolytically at ≑ pH 7.8. No such activity is detectable in any other part of the fore‐gut and tests for amylase and lipase are negative for all regions. Peptic action is first detectable about two days before the end of metamorphosis, approximately six days after the cessation of manicotto activity. The effect of the chemical nature of the type of food taken during ontogeny is considered. It is shown that the nature of the diet has no detectable effect on either the form or the physiology of the fore‐gut. The distribution of the manicotto is reviewed. It is concluded that the occurrence of the gland is neither a correlate of phylogenetic relationship nor of feeding habits but that its presence results from the protraction of the early anlage stage in the development of the larval pancreas. It is suggested that the absence of a peptic digestion in anuran larvae reflects a need for chloride ion economy in these forms.