Can anybody give me a pdf or note about the flatworms?

Flatworms

James H. Thorp, D. Christopher Rogers, in Field Guide to Freshwater Invertebrates of North America, 2011

B Reproduction and Life History

Some flatworms, especially those living in temporary aquatic habitats, reproduce only once per year (univoltine), while other species are multivoltine, with the number of generations depending on environmental favorability. Most flatworms reproduce sexually, and almost all species are hermaphroditic. Although gamete exchange is most common, self-fertilization is possible in some species. Eggs are laid singly on a hard substrate, are grouped into clusters (sometimes stalked), or are placed in cocoons. Miniature flatworms emerge from eggs which have been attached to the substrate. These usually develop directly (without intermediate larval stages) into adults and differ only in size and presence of reproductive organs. A few species are ovoviviparous (young brooded inside parent) or have a distinct larval stage. Asexual reproduction occurs seasonally in many taxa and is the only form of reproduction in a few species. This form of reproduction involves differentiation of the adult body into distinct units (zooids) followed by separation into small flatworms via transverse division of the adult body. This process is aided by the remarkable regenerative abilities of flatworms.

Under demanding environmental conditions, flatworms produce resistant eggs able to survive desiccation of the surrounding environment or the animal may enter diapause (a very low metabolic state) and encyst as a whole animal or fragment of the adult.

Sexually reproducing flatworms can live from a few weeks to a few months (not counting periods of encystment), while the life span of asexual species is theoretically indefinite.

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americans began to notice growing differences between the northern and southern sections of the country. there were more people living in cities in the north, which made it more urban. more people lived on farms in the south, which made it more rural. while many people were farmers in the northern states, there were now other ways to make a living, such as working in mechanical cotton gins factories manufacturing cloth, tools and other goods. people in the north supported high tariffs on goods imported from europe because the extra cost encouraged people to “buy american” instead. in the southern states, planters did not like tariffs because they sold most of their production to europe and bought their tools from there as well. southerners believed the protective tariff was something that only northern factory owners keep their profits high. so the southern politicians came up with an idea. they would opt out. they would simply ignore the protective tariff. it was ‘null and void’ in south carolina. the state would not collect the taxes on goods imported into south carolina, no matter what the president said they had to do. this decision led to the nullification crisis.