“The most essential Tleilaxu achievement, developed in rudimentary form long before Tleilax was discovered by the Guild, during the period when the Tleilaxu genetically manifactured lower forms – thralls, thirgoya and tharaxu – to “staff” their elaborate social order. The axolotl tank was thus the result of a long history of prior genetic research and development, in which the lower social forms served as experimental subjects.
Axolotl technology was not confined to the “tank” itself, which was little better than an artificial womb. The tanks were actually vessels for the end products and hosted a wide spectrum of activities centered on DNA recombination. After the experiment emerged from the axolotl solution, these results could be tested. The nature of this solution and of the tank was determined by the product being manufactured. The entire technology became increasingly refined and the demands of the Imperium increased.”
(da Dune Encyclopedia)