A Peritrophic Membrane in Calanoid Copepods

Abstract

FORSTER¹ has recently examined the peritrophic membrane in Caridea (Crustacea, Decapoda). He found a membrane in the mid-gut of all the Caridea examined and was able to show that it was chitinous. A similar membrane can easily be shown, to surround the fæcal pellets of calanoid copepods, where it often forms a ‘tail’, occasionally of considerable length, at each end of the pellet. That the pellet is indeed enclosed in a membrane can easily be demonstrated by compressing it carefully under a coverslip on a microscope slide. As pressure is applied the pellet first flattens more or less evenly throughout its length ; then the membrane suddenly ruptures at one point only and its contents can be seen streaming through the point of rupture. The membranes can also be demonstrated by careful heating of a pellet in a concentrated potassium hydroxide solution: the alkali dissolves most of the fæcal matter, leaving the membrane intact. No positive results were obtained in tests for chitin but this may well be because of the small size of the pellets (c. 1.5 × 0.15 mm.) and the delicacy of the membrane.