Tissues of cnidarian polyps have no permanent cell composition. During growth and development of the organism different types of the cells continually migrate from the places of their proliferation towards the location of their final functioning. Here we studied the role and mode of cell migration during development of the shoot internode in the colonial hydroid Gonothyraea loveni (Thecata, Campanulariidae). The internode formation starts with emergence of a new growing tip and ends by differentiation of a hydranth. We experimentally placed a ligature proximal to the growing tip to prevent tissue and cell migration towards the tip. A normal-shaped and viable hydranth was formed. However, the ‘experimental hydranths’ had problems opening the hydrotheca and lacked nematocytes. During the life of the ‘experimental hydranths’ no nematocytes appeared in their tentacles. When the ligature was removed, numerous nematoblasts and morular gland cells migrated towards the ‘experimental hydranth’ from the proximal part of the shoot coenosarc. Within a short time, the nematocytes appeared in the tentacles and the gland cells occupied the gastric region of the hydranth. This suggests that a subset of the cells migrate into the hydranth, during or after the final steps of its differentiation, from the proximal region of the shoot or from the stolon coenosarc. Our results also confirm the absence of cell proliferation in the hydranths of the thecate hydroid.