![]() ![]() We find that we have made a cnidarian coelenterate (OVERHEAD) Now if we simply flip this over through 180o All cells would retain a cilium, which would be used for The hole in the middle of the ball of cells and we might evenįind an inpushing, a cavity, a gut lined with digestive and absorbingĬells. The animal formed a dent with the new cells pushing upwards into Make it larger, and it is possible that to fit in more cells Local multiplication of cells in this area would LocalisedĬell division would perhaps be required to ensure an adequateįood supply. In this position we might find digestive cells. Which didn't get brushed aside as the organism rolled through To leeward and offered the opportunity of retaining food particles The side opposite the apical organ was now To happen was a preferred direction of swimming, with sensoryĬells collected at one particular place - lets call it the apical No special preference (OVERHEAD): probably the first thing How might aįree swimming blasteae cope better with swimming in the sea?Ī blastaea would roll through the water with Organisms live in water rather than ion the mud. Lets look now at an alternative scenario: many To the bottom, and that contact with the mud might set off aĬellular reaction leading to the defining of a ventral pole -Ī bottom end. We suggested that the organisation of thisĪnimal might be affected by its environment - that it might sink This will allow cells which don't feed to survive. This animal has a nice isolated cavity, the blastocoel cut offįrom the outside world and perhaps serving as a means of passageįor organic molecules from cell to cell without getting lost. (OVERHEAD) but probably with more cellular specialisation. Organisms blastaea, looking rather like a colony of choanoflagellates Last time we looked at the first metazoansĪnd the way in which we think they initially formed a hollowīall of cells with a cavity inside: we called these hypothetical ![]() The original authors are no longer at the University of Leeds, and the former Centre for Human Biology became the School of Biomedical Sciences which is now part of the Faculty of Biological Sciences. These pages have been left in this location as a service to the numerous websites around the world which link to this content. Evolutionary Developmental Biology Faculty of Biological Sciences, University of Leeds ![]()
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