Brij L. Gupta

Ultrastructural observations on the developmental cytology of the pituitary gland in the spotted newt

Abstract Observations have been made on the ultrastructure of the pituitary gland in the eastern spotted newt during embryonic, larval, and red eft stages. Secretory granules were first seen in the presumptive pars intermedia prior to hatching at a developmental stage equivalent to embryonic stage 40 of the harrison series for Amblystoma. In recently hatched larvae the cells of the pars intermedia reached definitive form, being characterized by granules of varying electron opacity. At this stage axon endings become apparent in both the pars nervosa and the pars intermedia. Up to the hatching stage the cells of the pars distalis were without granules but soon thereafter minute granules were apparent in some cells. By the premetamorphic stage agranular cells with elongate processes called stellate cells and a cell type with granules in the 180–250 mμ range were distinguished. Three more cell types appeared; one with smaller granules late in metamorphosis, one with a double population of granules in the first year eft and one with larger granules in the second year eft. The possible functions of these cell types are discussed.

Pogonophora: Uptake of Dissolved Nutrients

THE mechanism by which the marine tube-dwelling worms of the phylum Pogonophora obtain their food has remained obscure since Ivanov1 established that they have no conventional gut. Ivanov concluded that they are filter feeders, utilizing external digestion, while Carlisle2 has suggested that particles are actively picked up by the tentacles of the unitentaculate forms. Jägersten3 first put forward the idea that they absorb organic substances directly from solution, and this report provides evidence in support of his hypothesis.

Salivary gland development in the blowfly,Calliphora erythrocephala

The salivary gland of adult Calliphora erythrocephala is a tubular structure composed of secretory, reabsorptive, and duct regions. Development of these structures has been followed during the six days of larval and ten days of pupal growth. Two small groups of imaginal cells located at the junction between larval gland and duct give rise to the adult gland. These presumptive adult cells divide during all larval stages and appear to be functional components of the larval gland. Shortly after pupation, the larval gland breaks down and the imaginal cells proliferate rapidly, forming sequentially the duct, reabsorptive and secretory regions. Proliferating regions of the developing gland are frequently encrusted with haemocytes. As it elongates the gland establishes intimate contacts first with the basement membrane of the degenerating larval gland, later with an epithelial layer surrounding the main dorsal tracheal trunks, and then with the gut. Cell division continues until about five days after pupation, bu t the gland is unable to secrete fluid in response to 5‐hydroxytryptamine stimulation until two hours after the adult fly emerges. The Golgi complex appears to be involved in forming the highly folded membranes of the canaliculi in the secretory region.

Studies on Pogonophora. Fine structure of the tentacles

The structure of the tentacle in two species of Pogonophora (of the genera Nereilinum and Oligobrachia) has been investigated by light- and electron-microscopy. The fine structure of the pinnules, epidermal cells and mucous cells is described. The surface membrane of the epidermal cells and the pinnules forms an elaborate system of microvilli which traverse the cuticle and often extend up to the surface particles.