. Biology; the story of living things. THb: AllT OF PAllASITISM 229 the parasite, the plant is weakened and Httle or no grain is produced. A few of the wheat rusts do not require two hosts but complete their life cycle on wheat alone. Such rusts pass the winter by means of thick-walled spores which may remain in the stubble or in the ground until the young wheat plant appears the follow- ing year, or the spores are carried by the wind from other regions. Parasites Requiring More Than Two Hosts Tapeworms show a va- riety of adaptations and exhibit a unique and deli- cate balance that permits th
. Biology; the story of living things. THb: AllT OF PAllASITISM 229 the parasite, the plant is weakened and Httle or no grain is produced. A few of the wheat rusts do not require two hosts but complete their life cycle on wheat alone. Such rusts pass the winter by means of thick-walled spores which may remain in the stubble or in the ground until the young wheat plant appears the follow- ing year, or the spores are carried by the wind from other regions. Parasites Requiring More Than Two Hosts Tapeworms show a va- riety of adaptations and exhibit a unique and deli- cate balance that permits the completion of their various cycles. Roughly they may be divided into two groups, one in which the eggs reach water, sub- sequently passing through some aquatic organism, and a second in which ova are scattered in the soil and reach the intermedi- ate host by means of food or drink. In the first group are the broad tape- worm of man, the bass tapeworm, and many others, while the second includes the various tae- nioid worms and their relatives. All of these par- asites show a remarkable degree of N. Y. State Conservaiion Depi. The life cycle of the bass tapeworm {P. arnblo- plilis). (1) The mature tapeworm occurs in the intestines of the large- and small-mouthed hass. (2) Contact with water causes the proglottids to liberate the eggs which are eaten, (.3) by various copepods. \\ hen infected copepods are eaten by many species of plankton-feeding fish (1) a larval tapeworm (plerocercoid) develops in the mesenteries, liver, spleen, or gonads of these fish. Heavy infections in the small-mouthed bass affect reproduction. The tapeworm reaches maturity when fish infected with the larval stage are eaten by larger ones. How could this cycle be controlled in fish hatcheries!' The broad tapeworm of man, Diphyllobothrium latum, was brought to this country sometime during the last century by immigrants from the shores of the Baltic Sea. The worm matures in the digesti\e. P
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