Figure 1.

Puncture and inflation of hagfish skin. (a) Load at puncture for E. stoutii skin did not differ significantly (p = 0.930) from values from 21 other fish species when the significant covariate of skin thickness (p < 0.001) was considered, whereas extension at puncture (b) was slightly and significantly higher (p = 0.012). (c) Injection of hagfish Ringer's solution into the SCS and simultaneous measurement of hydrostatic pressure resulted in pressure–volume curves for 13 E. stoutii and six M. glutinosa specimens. The flat part of the inflation curve before pressure starts to rise provides a quantitative measure of an animal's flaccidity or ‘slack volume', which in both species was substantial relative to the animal's volume, but did not differ between species (p = 0.33). (d) Skin strain in the longitudinal and circumferential directions as a function of inflation pressure. At higher pressures, circumferential strain was 4.5 times higher than longitudinal strain, suggesting stiffer mechanical properties of the skin in the longitudinal direction.