[64] “I think it is probable that these cervical sclerites represent the hindermost of the cephalic somites, while the band with which the maxillæ are united, and the genæ, are all that is left of the sides and roof of the first maxillary and the mandibular somites.”--Huxley, Anat. Invert. Animals, p. 403. [65] Balfour, Embryology, Vol. I., note to p. 337. The following table shows the appendages of the head and thorax in the two classes. The homologies indicated are, however, by no means established.[66] CRAYFISH. | COCKROACH. | | Antennæ. ---- | ---- Eyestalks. | Antennules. | Antennæ. | Mandibles. | Mandibles. Maxillæ (1). | Maxillæ (1). Maxillæ (2). | Maxillæ (2). ---- | ---- Maxillipeds (1). | Thoracic Legs (1). Maxillipeds (2). | Thoracic Legs (2). Maxillipeds (3). | Thoracic Legs (3). [66] J. S. Kingsley in Q. J. Micr. Sci. (1885), has reviewed the homology of Insect, Arachnid, and Crustacean appendages, and comes to conclusions very different from those hitherto accepted. He classifies the appendages as pre-oral (Insect-antennæ) and post-oral, and makes the following comparisons:-- HEXAPODA. | ACERATA. | CRUSTACEA. | | (=Insecta | (=Arachnida | + Myriopoda?) | + Limulus.) | (1) Antennæ. | Absent. | Absent. (2) Mandibles. | Cheliceræ. | Antennules. (3) Maxillæ. | Pedipalpi. | Antennæ. (4) Labium. | 1st pair legs. | Mandibles. (5) 1st pair legs. | 2nd pair legs. | 1st Maxillæ. (6) 2nd pair legs. | 3rd pair legs. | 2nd Maxillæ. (7) 3rd pair legs. | 4th pair legs. | 1st Maxillipeds. Pelseneer (Q. J. Micr. Sci., 1885), concludes that both pairs of antennæ are post-oral in _Apus_, and probably in all other Crustacea. _Neck._ The neck is a narrow cylindrical tube, with a flexible wall strengthened by eight plates, the cervical sclerites, two of which are dorsal, two ventral, and four lateral. The dorsal sclerites lie immediately behind the head (fig. 14); they are triangular, and closely approximated to the middle line. The inferior plates (fig. 27) resemble segments of chitinous hoops set transversely, one behind the other, rather behind the dorsal sclerites, and close behind the submentum. There are two lateral sclerites on each side of the neck (fig. 27), a lower squarish one, which is set diagonally, nearly meeting its fellow across the ventral surface, and an oblong piece, closely adherent to the other, which extends forwards and upwards towards the dorsal side. _Thorax._