Allometrical studies in the brain of cyclostomes.

The brain weight - body weight relation was studied in 91 specimens of the order Cyclostomata (69 Petromyzonoidea, 22 Myxinoidea) and compared to data from other vertebrates. The interspecific slope of cyclostomes differs from that of other vertebrates (a = 0.23 in petromyzonts, a = 0.41 in myxonoids). Differences observed in the relationship of brain parts to body weight in the two suborders were interpreted as due to sense organ bound specializations. In a comparative diagram of the brain weight - body weight relation in vertebrates the cyclostomes take the lowest position.