more complex animals) build up the embryo. Drosophila melanogaster development Evidence for the syncytial theory can also be found in the development of Drosophila melanogaster. First 13 nuclear divisions take place forming a syncytial blastoderm consisting of approximately 6000 nuclei. During the later gastrulation stage, membranes are formed between the nuclei, and cellularization is completed. Criticism (synclital theory) The macro and micronucleus of Ciliates There is a lot of evidence against ciliates being the metazoan ancestor. Ciliates have two types of nuclei: a micronucleus which is used as germline nucleus and a macronucleus which regulates the vegetative growth. This division of nuclei is a unique feature of the ciliates and is not found in any other members of the animal kingdom. Therefore, it would be unlikely that ciliates are indeed the ancestors of the metazoans. This is confirmed by molecular phylogenetic research. Ciliates were never found close to animals in any molecular phylogeny. Flagellated sperm Furthermore, the syncytial theory cannot explain the flagellated sperm of metazoans. Since the ciliate ancestor does not have any flagella and it is unlikely that the flagella arose as a de novo trait in metazoans, the syncytial theory makes it almost impossible to explain the origin of flagellated sperm. Due to both the lack of molecular and morphological evidence for this theory, the alternative colonial theory of Haeckel, is currently gaining widespread acceptance. See also Multicellular organism Ciliate Evolutionary biology References Biological evolution