Microscopically, both undifferentiated and differentiated elements may be present. This decrease in cells is especially evident in the reduced number of undifferentiated mesenchymal cells. It is a squamous cell carcinoma of an undifferentiated type. A callus is mass of undifferentiated parenchymatous cells. Under defined conditions, embryonic stem cells are capable of self-renewing indefinitely in an undifferentiated state. These genes essentially maintain the stem cells in an undifferentiated state. It is critically involved in the self-renewal of undifferentiated embryonic stem cells. The subtypes were classified as&colon; paranoid, disorganized, catatonic, undifferentiated, and residual type. Histogenesis is the formation of different tissues from undifferentiated cells. Other parenchyma cells within the phloem are generally undifferentiated and used for food storage. All of these help to define the fate of undifferentiated cells in the embryo. The bracts transition into a perianth of undifferentiated tepals. These types have a more favorable prognosis than the medullary and undifferentiated types. As such, it is frequently used as a marker for undifferentiated cells. Metazoans do not include the sponges, which have undifferentiated cells.