Hank introduces us to the "simplest" of the animals, complexity-wise: beginning with sponges (whose very inclusion in the list as "animals" has been called into question because they are so simple) and finishing with the most complex molluscs, octopuses and squid. We differentiate them by the number of tissue layers they have, and by the complexity of those layers.
Crash Course Biology is now available on DVD! http://dft.ba/-8css
Like CrashCourse on Facebook: http://www.facebook.com/Yo
آی-ویدئو