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Quarterly Journal of Microscopical Science, Vol s3-93, 1-15, Copyright © 1952 by Company of Biologists
1 Dept. of Zoology, King's College, Newcastle-upon-Tyne
The body wall of A. lactifloreus has the following structure from the outside inwards.
(i) A basement membrane of five to six layers immediately underlying the epithelium. Each layer consists of right-hand and left-hand geodesic fibres making a lattice, whose constituent parallelograms have a side length of from 5 to 6µ. The fibres are attached to one another where they cross; so there can be no slipping relative to one another.
(ii) A layer of circular muscle-fibres running round the animal containing two systems of argyrophil fibres--one of fibres at intervals of 10µ. running parallel to the muscle-fibres and the other of fibres running radially through the layer from the basement membrane to the myoseptum.
(iii) A myoseptum which is identical in structure with a single layer of the basement membrane
(iv) A layer of longitudinal muscle, whose fibres are arranged in layers on each side of a series of longitudinal radial membranes.
Membranes identical in structure with the basement membrane invest the nerve cords, the gut, the gonads, and the proboscis.
The interrelations of argyrophil and muscle-fibres in the muscle layers is described and their functioning discussed.
The system of inextensible geodesic fibres is analysed from a functional standpoint. The maximum volume enclosed by a cylindrical element (cross-section circular), of such a length that the geodesic makes one complete turn round it, varies with the value of the angle 
between the fibres and the longitudinal axis. When is 0° the volume is zero; it increases to a maximum when is 54° 44' and decreases again to zero when is 90°. The length of the element under these conditions varies from zero when is 90° to a maximum (the length of one turn of the geodesic) when is 0°.
The body-volume of the worm is constant. Thus it has a maximum and minimum length when its cross-section is circular, and at any length between these values its cross-section becomes more or less elliptical. It is maximally elliptical when is 54° 44', i.e. when the volume the system could contain, at circular cross-section, is maximal. From measurements of the ratio of major to minor axes of this maximally elliptical cross-section, the maximum and minimum lengths of the worm relative to the relaxed length and values of at maximum and minimum length are calculated. The worm is actually unable to contract till its cross-section is circular; but measurements of its cross-sectional shape at the minimum length it can attain, permit calculation of the theoretical length and value of for this cross-sectional shape.
Calculated values of length and the angle 6 agree well with the directly observed values.
