Morphology and development of the salivary glands and their chromosomes in the larvae of Anopheles stephensi sensu stricto.

In the larvae of Anopheles stephensi s. s. five typically banded salivary chromosomes are present united proximally to a chromocentre. Maps have been constructed to illustrate their constant and characteristic banded pattern. Chromosome IIIR, however, has shown a variation in the form of a heterozygous inversion. The chromocentre is a small, fragile body, closely associated with the large nucleolus.The development of the salivary glands in the larva is by cell-growth. The chromocentre appears at first as a heteropycnotic "crescent", which soon gives place to a disc-shaped body. Later on in development the chromocentre loses both its heteropycnotic nature and compactness. The nucleolus persists until the time of histolysis of the glands, which begins at the distal end of the gland and gradually involves the more anterior regions. At the earliest observable stage the homologous chromatin elements constitute a tight coil. Full synapsis is preceded by a process of uncoiling accompanied by a chromomere-to-chromomere fusion. The rate of this process varies among different pairs of homologues and along different regions of the same pair. Synapsis is completed in the late third instar larva.RNA is localized in the cytoplasm and the nucleolus of the larval salivary gland cells. The chromosomes and the chromocentre include DNA. A faint reaction of the interband areas show that DNA is present in a diffuse state throughout the chromosomes.