Ultrastructural observations and histochemical analyses show the presence of immature nematocysts within the cnidosacs of the aeolid nudibranch
Spurilla neapolitana. Quantitative and ultrastructural analyses indicate that the immature nematocysts mature within the cnidosacs. The incorporation of unfired immature nematocysts may be the basic mechanism that permits nematocyst uptake, storage and utilization by nudibranchs.
Communicated by J. M. Lawrence, Tampa