End of p. 378 goes together with p.379, inappropriate separation
(13) Even though …..
In fact, there are two distinct levels that are relevant to language: in the formation of the latent structure and in the actualization process from latent to realized structure. The former may be due to variations in the operation of cognitive processes or due to variations in the maturational course; the latter is primarily due to variations in peripheral function and structures such as the vocal tract of the ears. Variations on these two levels explain the main facts about language constancies, language change, and language universals.