H. nigrescens (Egg Sacs) (Hasumi)

A Pair of Egg Sacs of Hynobius nigrescens

Two egg sacs, composed of a pair of right and left ones, at the stage of tail bud (Hynobius nigrescens). A spindle-shaped egg sac is characteristic of H. nigrescens, which is unknown in other hynobiid species (e.g., Egg Sacs of Hynobius hidamontanus; Egg Sacs of Hynobius kimurae). Although egg sac coloring varies within a geographic range, the majority of which is an opaque-white type, a transparent type of egg sacs as shown in this photograph occurs occasionally. An egg sac just deposited in the water has a size of the little finger of the adult man (mean mass of 26 egg sacs is approximately 2.7 g), jelly layers of each egg sac absorb water gradually, and egg sac mass increases to 180.6 g in average just before hatching (it takes about 37 days until hatching at 8 C; Hasumi et al., 1994). The number of eggs in a pair of egg sacs (i.e., a full clutch) varies markedly among populations, e.g., ca 100.6 eggs (n = 38) in Iwamuro-mura (180 m elevation), ca 53.6 eggs (n = 8) in Ohshima-mura (760 m elevation), and ca 56.0 eggs (n = 6) in Shibata-shi (1100 m elevation), each population being in Niigata Prefecture, Japan (Hasumi, 2001).