Scanning electron microscopy revealed the presence of a number of cuticular sensillae on the head of different larval stages of the "Muga" silk moth, Antheraea assamensis. These include four types of sensilla trichodea, bead-like folded sensilla, two types of sensilla basiconica, and sensory pegs. The study seems to be the first attempt in describing the morphology and distribution pattern of the cephalic cuticular sensillae of different larval stages of the silk moth Antheraea assamensis, an indigenous species of Northeast India. The possible significance of the sensillae in searching behavior of the larval stages during feeding is discussed with the help of available literature.
Small graft pieces (size: 0.15xO.2mm to 0.1 x0.4mm and 0.25x0.25 mm) were isolated from the prospective prosencephalic ectoderm of the definitive primitive streak (st. 4) and head process (st. 5) chick blastoderms, and cultured in vivo intracoelomically. In all 1437 graft pieces isolated from 448 donor blastoderms were transplanted into the coelom of 941 host embryos; 216 hosts died before reaching 12 days. The 725 surviving hosts, which carried 1241 implants, yielded 304 analysable grafts. The very small size of the isolates affected the recovery rate. The histological analysis of the recovered grafts reveals that the frequency of neuralization was higher in the grafts isolated from the central region of the prospective prosencephalic ectoderm than in those from its peripheral region. A centrifugal extension of Merentiation tendencies of prosencephalic structures was observed from st. 4 to st. 5. At st. 5 frequency of telencephalic structures was high in the grafts of the anterior region, whereas that of diencephalic structures was high in those of the more posterior region. Eye structures (retina as well as tapetum) differentiated in an area measuring ca. 0 . 4~0 . 1 mm extending transversely about 0.1 mm anterior to the head process at st. 5.Structural elements of the lens were not observed in any graft.Attempts to understand the process of neural induction in the early chick embryo date back to the work of WADDINGTON (1 , 2), who first proposed the role of the head process mesoderm as neural inductor. HARA (3), based on his sandwich experiments, demonstrated that prechordal mesoderm induces prosencephalic differentiation tendencies in the competent ectoderm; anterior part of the head process induces mes-/rhombencephalic differentiation tendencies ; while its posterior part induces rhombencephalic and spinal cord differentiation tendencies. RAO (4) analysed the pattern of appearance and extension of regional differentiation tendencies in the prospective neural ectoderm. However, his isolates were large in size (e.g. his median piece covered 3/4 of the width of the prospective neural ectoderm) and he did not study differentiation tendencies of various,components of the brain in more detail. In the present work, differentiation tendencies of much smaller pieces of prospective prosencephalic ectoderm have been tested; and an attempt has been made to analyse the pattern of neural differentiation in this region. Special attention has been paid to the localization of the eye potency field, and results are discussed in comparison with the earlier findings (5, 6, 7), which were based on the differentiation of test pieces comprising all three germ layers.
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The lateral aspects of larval cephalic cuticle of oak tasar moth, Antheraea proylei, a hybrid between Antheraea pernyi and Antheraea roylei exhibited the presence of gravity receptors in the form of dorsal campaniform sensilla. The distribution pattern and number of dome shaped dorsal campaniform sensilla were found to vary in different larval stages. In the first and second larval stages, 4-5 sensilla were localized near the apex of the lateral aspects of the cephalic cuticle on either side of the head. From the third larval stage onwards, on the other hand, both the right and left lateral aspects of the cephalic cuticle were covered with innumerable dome shaped dorsal campaniform sensilla. The sensilla were found to be arranged in groups of 3 to 5 on the cephalic cuticle with dome-free cuticular portion of about 50-100 µm in length between two adjacent groups of the sensilla. The individual dome shaped dorsal campaniform sensillum was either smooth surfaced or was covered with smaller domes through out the surface. The significance of differences in the number and distribution pattern of the dorsal campaniform sensilla among different larval stages in relation to gravity reception and preferred feeding posture are discussed in the light of available literature.
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