Secretory discharge and microflora of milk gland in tsetse flies

Abstract

THE uterine or milk glands in tsetse flies (Glossina spp.) are modified female accessory reproductive glands which elaborate and release a nutritive liquid of proteinaceous and lipoid nature for the maturing intrauterine larva^1–3. The multi-branched tubules of the gland converge into a pair of efferent ducts which fuse inside the oviductal shelf and open into the lumen of the uterus just posterior to the opening of the oviduct^4,5. Cytological details of the milk gland and their modulations in relation to the state of pregnancy of the female have been described⁶ (W-C. M., D. L. D., D. S. Smith and U. Jarlfors, in preparation). Earlier work has suggested that milk is released directly into the lumen of the gland by apocrine secretion⁴. Our observations on the structure of the milk gland do not support such a mechanism, but rather, a novel type of exocrine discharge in which secretion is stored in an extracellular reservoir and released into the lumen through a dense cuticular network. At the points of milk release the lumen is frequently inhabited by bacteria which have not previously been described in milk glands. Our examination is based on milk glands from G. morsitans morsitans West-wood, but a comparative study using G. austeni Newstead and G. longipalpis pallidipes Austen has shown no essential differences among the three species.