A Glimpse into the Life History of the Tapeworm of Sheep, Moniezia expansa

Abstract

To date there has been nothing known of the life history of Moniezia expansa. In the present paper, I give an account of my studies on the eggs which show quite distinctly the way sheep become infested with this parasite. My observations begin from the moment when eggs, enclosed in the body of ripe segments, leave the intestine of the sheep with the excrements and ends at the forty-fifth day of their being at large and outside of any host. The main features of an egg, taken from a ripe segment, are shown in figure 1. The shape is nearly that of a regular hexahedron, with all its angles rounded off. The shell is composed of three envelopes or coats: the exterior (h, Fig. 1) is hard and non-elastic, horny and indissoluble in the digestive fluids though permeable to water; the interior (i) is soft and of a fibrillar structure; the intermediate (o) consists of small drops of an oily substance, and is the thickest of all. The horny coat meets the fibrillar at the angles of the egg, so that the oily coat is distributed only on the sides of the hexahedron, being absent at the angles. Inside the shell, there is lying loosely a structure, known under the name of the pyriform, or pear-shaped apparatus; this will be called the capsule. In the capsule can be distinguished two portions: the body, which is spherical, and the horns, which are cylindrical, gradually tapering to their ends. The substance of the capsule is homogeneous, perfectly translucent, elastic, permeable to water and dissoluble in the digestive fluids, including the saliva, and, under certain conditions, in mucus of respiratory cavities. The walls of the capsule grow thinner toward the top of the capsule, being thickest at its base where the pair of horns arise. Inside, the body of the capsule is divided into two compartments: the upper, where the embryo is enclosed (e) and the lower that contains an apparatus for feeding the horns (s, f). Both horns are of equal size and shape. They are slightly bowed and bear a common cap (c) at their distal ends. The feeding apparatus of the horns consists of two protoplasmic and nodular strings, one for each horn, and of two granular cells, which belong only to one of the horns. The strings are attached to the ceiling of the lower compartment and stretch along the canals of the horns up to their ends.