Roy L. Hughes

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Information on the pre-hatching development of the platypus, Ornithorhynchus anatinus, is reliant on a small number of specimens, whose precise age is unknown. Material collected for J. P. Hill and now housed in the Hubrecht International Embryological Laboratory, Utrecht, contributes a major source of specimens. This paper presents new observations on(More)
The elongated spermatid nuclei of monotremes exhibit a circumferentially arranged spiral pattern of chromatin condensation, and ultimately form helical filiform sperm heads up to 50 μm long and either circular or slightly oval in transverse section. The acrosome is formed by the collapse of the proacrosomal vacuole onto the rostral surface of the elongating(More)
This paper considers many of the salient features of monotreme development, particularly morphogenesis of the extraembryonic membranes. The uterine endometrium of both monotremes and marsupials exhibits a progesterone driven luteal phase where accelerated utilization of endometrial nutrients is evidenced by a rapid post-primitive streak expansion in the(More)
Pigmented spots have been implicated as potential photoreceptors in many bryozoan larvae which display phototactic behavior. Larvae ofScrupocellaria bertholetti, initially photopositive on release from the brood chambers, have a pair of identical posterolateral pigmented spots and a third morphologically different spot in the anteromedian line. The presumed(More)
In marsupials testis determination requires the presence of a Y chromosome. The sex determining region on the Y gene (SRY) is necessary for testicular development in eutherians and it is assumed to play a similar role in marsupials. Relatively few studies have investigated the genetic basis of sexual development, and as yet there is no direct evidence that(More)