Note 11 — Chapter IV · THE MORPHOLOGY OF THE COM­MON CRAY­FISH: THE STRUC­TURE AND THE DE­VEL­OP­MENT OF THE IN­DI­VI­DUAL.

There are some singular marine crustacea, the Squillidæ, in which both the ophthalmic and the antennary somites are free and movable, while the rostrum is articulated with the tergum of the antennary somite.