Fig. 184.—Schematic representation of a small part of a transverse section of Ligula sp. Bs., basal membrane; Cu., cuticle; at its base are the endplates of the subcuticular (epithelial) cells; in the centre a cuticular sense organ, O.s.; F.v.s., vitelline follicle; Exc., excretory vessel; C., calcareous corpuscle; L.m., longitudinal muscles; M.c., myoblast; P.m., parenchymatous or dorso-ventral muscles; Pl., plexus of nerve fibres; A.m., circular muscles; Sc.c., subcuticular or matrix cell; T.c., terminal flame cell. 500/1. (After Blochmann.)
In addition to the above mentioned, there are other cuticular formations occurring on the cuticle of some Cestodes, such as immobile hairs and variously formed hooks, such as are seen principally on the scolex. Their development is only roughly known in a few species; they are usually already present in the larval stage, and of the same arrangement and shape as in the fully developed tapeworms; a matter of importance, because by these structures larvæ can be recognized as being those of a certain species of tapeworm.
The CUTICULAR GLANDS in Cestodes are scarce.
The PARENCHYMA forms the chief tissue of the entire body, and in all essentials its structure is similar to that of the Trematodes.
The same doubt exists here also as to the nature of the parenchyma. Recent authors consider that it consists of highly branched cells, the processes of which ramify in all directions. These cells lie in a non-cellular matrix containing fluid vacuoles. This matrix spreads in between and so breaks the continuity of the epidermal cells.
In the parenchyma of almost all the Cestodes there are found in adult specimens, as well as in larvæ, light-refracting concentrically striated structures, of a spherical or broad elliptical shape, which, on account of their containing carbonate of lime, are termed CALCAREOUS CORPUSCLES (fig. 184, C.). Their size, between 3 µ and 30 µ, varies according to the species; their frequency and distribution in the parenchyma also varies, but they are chiefly found in the cortical layer. They are the product of certain parenchymatous cells, in the interior of which they lie like a fat globule in a fat cell, but according to others they are intercellular in origin.
The MUSCULAR SYSTEM of the proglottids is composed of—(1) the subcuticular muscles (figs. 184 and 185), as a rule consisting of a single layer of annular muscles; (2) longitudinal muscles; (3) dorso-ventral fibres extending singly from one surface to the other, and at both ends expanding in a brush-like manner, and inserted into the basal membrane, consisting of an outer, more numerous, and an inner, less numerous but more powerful layer (the number of bundles in this layer being in certain cases of specific importance); (4) transverse fibres, the elements of which penetrate to the borders of the segments, thus passing through the longitudinal muscles and reaching the cuticle. In the region of the septa the transverse and dorso-ventral muscles form a kind of plate.
