[Cellular ultrastructure of developing conglomerates of fresh water sponges]

The fine structure of cells of the conglomerates formed after dissociation of tissues of fresh-water sponges has been studied. In the development of the conglomerates of Ephydatia fluviatilis an important role is played by amoebocytes and choanocytes. In amoebocytes the shape of the nucleus, the mitochondria structure, the Golgi complex and endoplasmic reticulum have been found to change. In choanocytes, in addition to changes of organoids, the structure of the collar and flagella are subjected to desorganization. They have great plasticity and are able to re-differentiate in pinacocytes according to their position in the conglomerates. The transformation of amoebocytes and choanocytes into pinacocytes is accompanied by a successive modification of the nucleus and the cytoplasmic structures. In redifferentiation of amoebocytes the amount of Golgi apparatus zones decreased, the content of vacuoles of different size and the amount of elements of the agranular endoplasmic reticulum increased, and the defined nucleus disappeared.