The first and second abdominal sterna are often suppressed or reduced, on account of the strong development of the hind-legs.
Ileymons, the hypopharynx represents the sterna of all the jaw-bearing somites, but other students consider that it belongs to the mandibular and first maxillary segments, or entirely to the segment of the first maxillae.
In the abdominal exoskeleton the segmental structure is very clearly marked, a series of sclerites - dorsal terga and abdominal sterna - being connected by pale, feebly chitinized cuticle, so that considerable freedom of movement between the segments is possible.
To Turner's name, repeated by Gesner and other authors, we owe the introduction by Linnaeus of Sterna into scientific nomenclature.
The more common sea-birds are the Sula variegate or guano-bird, a large gull called the Larus modestus, the Pelecanus thayus, and the Sterna Ynca, a beautiful tern with curved white feathers on each side of the head.
It is without doubt the Sterna of Turner, and in former days was abundant in many parts of the fen country,' to say nothing of other districts.
This last is the beautiful roseate tern, Sterna dougalli; the other is the black tern, Hydrochelidon nigra, belonging to a genus in which the toes are only halfwebbed, of small size and dark leaden-grey plumage.