The femal specific proteins (FSP) identified in the hemolymph of Squilla mantis females are here proven to be vitellogenins (VTG) by immunological and electrophoretical methods. VTG 1 which has a higher molecular weight (MW) and only one central form, both in hemolymph and eggs, can be detected immunoelectrophoretically. VTG 2 and 3 have similar lower MW and are immunologically closely related, their slightly cathodic precipitation are fusing with the slightly anodic form. A further cathodic shift of the double arc occurs in the corresponding egg proteins. The VTGs are forms of yolk proteins which are transported in the hemolymph from the site of synthesis to the ovary where they undergo structural variations without involving a change of MW or of their number.