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In continuing this record it is, perhaps, as well that I should remind the members of the Section that the Cestodes differ essentially from the Trematodes in that the so-called species are multiple in character. What is spoken of as a tapeworm is not one creature, but in reality a multitude of organisms, or zooids, arranged in single file. The head itself is merely the topmost zooid, modified in shape. and armed with sucking disks, so as to form a means of anchorage for the whole colony. This cephalic holdfast, as it might be called, is in some sense the counterpart of what we see not only in the fixed polypes, but also in the free compound madusæ. In carrying out the analogy it must net be forgotten that the solid hydrorhiza of an ordinary Sortularian polype was once a free swimming ciliated larva, whilst the inflated end of the cœnosare forming the float of Physalus had a similar origin. In all these cases the metamorphosis of a larva, either directly or indirectly, secures the formation of an organ of anchorage or support involving the welfare of the entire chain or colony of zooids. It is sufficient to insist upon the strict analogy of these phenomena without suggesting questions of homology. An ordinary human tapeworm (such, for example, as that derived from eating measled beef) consists of about twelve hundred zoids, or proglottides. Each progloitis is bisexual, and, when mature, is capable of holding, according to Leuckart, about 35,000 eggs. The entire colony of twelve hundred zooids is renewed every three months, and thus if follows that the amount of egg-dispersion annually resulting from a single beef-tapeworm cannot be less than twelve millions. In all probability this calculation is very much below the mark, seeing that the 35,000 impregnated germs capable of existing in the fully mature proglottis, at a given period, do not by why means serve to fix the limit of the possibilities of egg-formation within the peoglotiis. Of course, as compared with the quantity of germs distributed, the number that survive and come to perfection, as Tæniæ, must be infinitesimally small.

13.—Tænia mediocaneltata, Küchemeister.