The blood vessels supplying the central nervous system of the earthworm are of the same type as those in the brains of tailed amphibians, lizards, and marsupials, i.e. the blood vessels are paired and end in loops. The blood vessels in the cerebral ganglia of the squid form a network like that which occurs in the brains of fishes, anuran amphibians, reptiles (except lizards), birds, and placental mammals. The origin of both systems is discussed.
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E. Scharrer (1944) studied this question.