Number of Neoblasts in the Intact Body of Euplanaria torva and Dendrocoelum lacteum
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The regeneration, blastema in planarians is constituted by the totipotent neoblasts which migrate to the wound (Dubois, 1949). The rate of regeneration, measured by appearance of eyes in the blastema, shows a characteristic variation throughout the planarian body, thus constituting a static, time-graded regeneration field (Brondsted, 1946). We do not know the mechanism underlying this species-specific feature. Neither do we know why some species, e.g. Dendrocoelum lacteum , are able to regenerate a head only from the part of the body lying anteriorly to the pharynx, whereas other species, e.g. Euplanaria torva , can regenerate a head from almost every part of the body. A possible explanation might be the number of available neoblasts. This idea was formulated by Curtis & Schulze (1934). They claim that in Procotyla fluviatilis , a species closely related to D. lacteum , the inability to regenerate a head from parts behind the pharynx is due to scarcity of neoblasts, as compared with species with greater regeneration ability.