Sir A. E. Shipley, The Cambridge natural history, Vol… (1909)
“ It has been usually held that the indefinite number of segments characteristic of the Entomostraca, and especially the indefinitely large number of segments characteristic of such Phyllopods as Apus, preserves the ancestral condition from which the definite number found in the Malacostraca has been derived; but recently it has been clearly pointed out by Professor Carpenter [3] that the number of segments found in the Malacostraca and Leptostraca corresponds with extraordinary exactitude to the number determined as typical in all the other orders of Arthropoda. ”
