Table S1.

Experimental values and estimates that are referenced throughout the text

Quantity	Value	Source
Duration of total fission process	17.8 ± 10.1 min (n = 17)	Measured duration between initiation of waist formation and rupture
Young’s modulus of worm shell (E)	500 Pa	16
Planarian shell thickness (hshell)	10 µm	14
Mucus layer thickness (hmucus)	10 µm	16
Planarian waist radius (RWaist)	0.31 ± 0.06 mm (n = 22)	Half the measured width of the waist region
Planarian head radius (R)	1.2 ± 0.1 mm (n = 22)	Half the measured width of the head piece before pulsation begins
Planarian density (ρ)	1,000 kg/m3	See description of density measurement in Materials and Methods
Planarian head volume (VH)	22 ± 11 mm3 (n = 22)	Assuming a cylindrical worm, ${\mathit{V}}_{\mathit{H}}=\mathit{\pi }{\mathit{R}}^2\mathit{L}$, where R and L are the measured worm head radius and length, respectively
Planarian–substrate contact area (Acontact)	8.7 ± 3.3 mm2 (n = 22)	Measured manually as the area of the worm head profile when imaged from above
Mucus viscosity (η)	65 Pa·s	See Fig. S6B and description of mucus rheology in Materials and Methods
Stress amplification factor $\left({\mathit{A}}_{\mathbf{Head}}/{\mathit{A}}_{\mathbf{Waist}}\right)$	14 ± 3 (n = 22)	Assuming both cylindrical head and waist, we have ${\mathit{A}}_{\mathit{H}}/{\mathit{A}}_{\mathbf{Waist}}={\mathit{R}}^2/{\left({\mathit{R}}_{\mathbf{Waist}}\right)}^2$
Pulse extension velocity $\left({\mathit{v}}_{\mathit{ext}}\right)$	1.1 ± 0.4 mm/s (n = 16)	Using values from logistic fits of extension described in Materials and Methods
Contraction duration $\left({\mathit{\tau }}_{\mathit{cont}}\right)$	44 ± 20 s (n = 18)	Measured duration of the linear contraction phase of pulsation
Maximum longitudinal strain (ε)	0.43 ± 0.15 (n = 16)	Using values from logistic fits of extension described in Materials and Methods, $\mathit{\epsilon }=\mathrm{\Delta }\mathit{L}/{\mathit{L}}_0$
Traction stress on substrate (σ)	100 Pa	Measured from traction force experiments; value reflects the order of magnitude of measured stresses
Radial contraction $\left(\delta R\right)$	0.27 ± 0.13 mm (n = 16)	Difference between maximum and minimum radius in the head during pulsation

This table describes the characteristic values of relevant experimental parameters. The Source column lists either the relevant reference from the literature or the method of calculation and/or measurement. Entries in the Value column that stem from experiment are average values and accompanied by ±SD.