placodes (plak´ōds), the thick, flat sections of embryonic ectoderm on the facial surface of the embryo from which the sense organs develop.
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mice lacked two pairs of placodes, and other pairs that formed were small and degenerated during mammary gland development (van Genderen et al.
mice displayed an abnormal phenotype, which failed to develop most mammary placodes (Davenport et al.
Gibson and his colleagues instead found that starlet sea anemones (Nematostella vectensis) form tentacles from thick patches of cells called placodes.
The lens placodes form the lenses of the eyes in week 5, and the primary lens fibers reach the anterior wall of the lens vesicle by the end of week 7.
Stage Y&K Description 1 14 Late gastrula 2 16 Head fold 3 17 Optic vesicle 4 20 Optic cups 5 21 Auditory placodes 6 22 Lens 7 23-25 Otoliths, heartbeat, black pigment in retina and iris is strongest in periphery.
Vertebrate structures such as the neural crest and the placodes further the development of the head and the brain, which reaches an unprecedented complexity in humans.
Londt (1983)--Revised Daspletis, presenting a key to six species: hermanni (transferred from Microstylum), hirtus, setithoracicus (established within the genus as a consequence of the synonymy of Neodysmachus), vulpes, and two new species, placodes and stenoura, both from South Africa.
Antennae 30 antennomeres, longer than body, the basal flagellomeres about 3 times as long as wide, the following slightly shorter, Fp about 2 times as long as wide; the setae as long as the segment width; in lateral view 3 placodes visible.
The nasal placodes (olfactory placodes) arise from the medial aspect of the lower portion of the frontal prominence, and the lens placodes arise from the lateral aspect of the lower portion of the frontal prominence.
At E12, the feather placodes (short bud) were clearly visible on the skin surface, the feather placodes of the dorsal tracts were of different sizes; while the feather placodes on the thoracal and ventral tracts were smaller and distributed regularly.
The nasal placodes develop as early as the third week of gestation.
Vertebrates have three types of embryonic tissue not present in invertebrates: neural crest cells, ectodermic placodes, and a modified paraxial mesoderm.