In hydra, nerve cells are a differentiation product of the interstitial cell, a multipotent stem cell. Nerve cell commitment was examined during head regeneration in Hydra attenuata. Within 3 h of head removal there is a 10- to 20-fold increase in nerve cell commitment in the tissue which subsequently forms the new head. Nerve cell commitment is unaltered in the remainder of the gastric region....

The purpose of this paper is to analyze the effect of constant effort harvesting upon global dynamics of a discrete-time population model with juvenile and adult stages. We consider different scenarios, including adult-only mortality, juvenile-only mortality, and equal mortality of juveniles and adults. In addition to analytical study of equilibria of the system, we analyze global dynamics by m...

S-phase cells in intact animals of the coelenterate species Eirene viridula, Hydractinia echinata, Hydra attenuata, and Hydra magnipapillata incorporate the thymidine analogue bromodeoxyuridine (BrdU) into newly synthesized DNA. BrdU-labelled nuclei divide and cells appear to undergo normal differentiation. Whole-mount preparations and macerated tissues were screened for S-phase cells by means ...

Twenty-three species of silicified brachiopods are described from four samples in the middle and upper parts of the Episkopi Formation from Hydra Island, Greece. These brachiopods are newly recorded from the region and together with previously described brachiopods from the same localities constitute the most diverse Lopingian (Late Permian) brachiopod fauna reported in southern Europe. The bra...

‘I want to ground my discussion of explanation in biology in that which leads biologists to say Aha!’ says Evelyn Fox Keller, professor of the history and philosophy of science at the Massachusetts Institute of Technology. Keller is fascinated by biologists’ explanations of their work. But she is also interested in how biologists have managed to be so extraordinarily successful over the past ce...

The steady-state relative population sizes of the several cell populations in Hydra attenuata were examined. In contrast to the constant average population size ratios between groups of animals, these ratios vary within limits between individual animals within a group. By maintaining animals on different feeding regimes (number of shrimp larvae ingested per day), the steady-state population si...

Despite initiatives and actions, only minor steps towards better communication systems have been achieved in healthcare. We examine this phenomenon empirically through three Norwegian healthcare projects, all of which started in 2005. The projects were initiated and funded by the Norwegian government and were aimed at establishing inter-organizational integration in healthcare. We examine the n...