(1) The regions of lab expression in the developing cephalon represent nonsegmented domains that are anterior to and largely nonoverlapping with the domains of expression of the Deformed (Dfd) and proboscipedia (pb) genes, two other homeotic loci of the ANT-C that also function to direct the development of head structures.
(2) Experiments carried out with different tissue extracts have shown that this activity occurs in the cephalon, more exactly in the laterooesophageal glands.
Trilobite
Definition:
(n.) Any one of numerous species of extinct arthropods belonging to the order Trilobita. Trilobites were very common in the Silurian and Devonian periods, but became extinct at the close of the Paleozoic. So named from the three lobes usually seen on each segment.
Example Sentences:
(1) In which case, now you suddenly realise that trilobites have bloody good eyes, so maybe they were there too!
(2) Wow!” (Graptolites and trilobites are long-extinct marine animals).
(3) The thick lenses in the aggregate eyes of a group of trilobites were double structures designed to eliminate spherical aberration.
(4) Permian-Triassic, c 250 million years ago The big one – more than 95% of species perished, including trilobites and giant insects – strongly linked to massive volcanic eruptions in Siberia that caused a savage episode of global warming.
(5) Trilobites may have evolved such sophisticated eye-lenses to maximise optic neurone response in a dimly lit environment.
(6) The shape of the aspherical interface in the cornea of some phacopid trilobites with schizochroal eyes is investigated.
(7) On the basis of the geometric optical method presented, the refractive indices and focal length of the original corneal lenses of trilobites can be determined.
(8) Here I report some of the first detailed evidence of phyletic gradualism in benthic macroinvertebrates, based on a study of approximately 15,000 trilobites from central Wales.
(9) The question posed, the geometric optical method used and the results presented are of general importance, and not only with respect to vision in the bug Notonecta, but also in the fossil trilobites, or in the wave guide theories which have been employed in similar modelling problems, in design of system of lenses without spherical aberration, for example.