IN previous communications (see Huxley, 1927, Biol. Zentralbl., 47, 151) it has been pointed out that in Crustacea the presence of a centre of active growth, for example, in a male chela, is associated with excess growth of the other walking legs. The third maxilliped, however, is not affected in this way, but appears to be slightly decreased in the male. The question arose whether this was a positional effect, appendages anterior to the growth-centre being inhibited in their growth, those posterior being accelerated, or whether, since the maxilliped was an appendage of different type from the pereiopods, its growth was not correlated with theirs.