. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 234 THE TAPEWORMS for instance, the male reproductive system reaches maturity when the proglottid has been pushed back to about the 200th position, whereas the female system does not mature until it has been pushed 200 or 300 proglottids farther back. Copulation then takes place by the doubling back of the chain of proglottids on itself, bringing the young mature male segments into contact with the older mature female segments. After copulation, when the mature fertilized eggs begin to form, great chang
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 234 THE TAPEWORMS for instance, the male reproductive system reaches maturity when the proglottid has been pushed back to about the 200th position, whereas the female system does not mature until it has been pushed 200 or 300 proglottids farther back. Copulation then takes place by the doubling back of the chain of proglottids on itself, bringing the young mature male segments into contact with the older mature female segments. After copulation, when the mature fertilized eggs begin to form, great changes take place in the proglottid. The uterus begins to enlarge and branch until it nearly fills the segment, crowding aside and absorbing the other organs. Segments thus distended with eggs are spoken of as " ripe " proglottids and are ready to break loose from the chain to be voided with the faeces of the host. Ripe proglottids of a number of species of tapeworms found in man are shown in Fig. 84. Life History. — The life histories of all tapeworms are much alike. Usually before the ripe proglottids become detached and pass out of the host, the eggs develop, inside their tough shell, into little round embryos with six hooks (Fig. 85A). In order to continue their Fig. 85. A, egg of beef tapeworm, T. saginata; j i + V» — note contained embryo and external filaments; development SUCU em- B, freed six-hooked embryo. X 300. (After bryOS must be eaten by Leuckart.) ,1 • r • 1 another species oi animal which acts as an intermediate host. Most often the adult form of the worm occurs in carnivorous animals, while the in- termediate host in which the larva develops is a herbivorous animal, but there are numerous exceptions to this. There is no active search for a new host on the part of the tapeworm embryo as there is by the embryos of flukes, but instead merely a passive transfer. When eaten by a suitable intermediate host, the shell enclosing the six-hooked embryo is
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmedical, bookyear1918
