Secondary mesenchyme cells clearly exert tension where they attach, pulling out what T. Gustafson called "cones of attachment" . When a filopodium detaches, such cones rapidly snap back, indicating that the filopodia were exerting tension where they were attached.
To see a movie of a high magnification view of such attachments forming and breaking, click on the picture below. The arrow in the picture denotes a cone of attachment.
Size of movie: ??? K