Ultrastructure of cuticle formation in the nematodes Nippostrongylus brasiliensis and Nematospiroides dubius.

The ultrastructure of cuticle formation was studied in the third molt of Nippostrongylus brasiIiensis, a parasite of rats. For comparative purposes, early events in the formation of adult cuticle during the fourth molt of Nematospiroides dubitts, a parasite of mice, were also examined. In the former, the third cuticle became separated from the hypodermis plasma membrane, and a filamentous coat was deposited on the external surface of the membrane. The surface coat increased in size and the hypodermis plasma membrane folded regularly to form plicae which circumscribed the worm. An inner layer was deposited between the hypodermis plasma membrane and the filamentous outer layer, which in turn differentiated into the triple-layered limiting membrane of the fourth cuticle. Corresponding events in formation of adult cuticle in N. dubius were similar to those seen in N. brasiliensis. These observations indicated that the cuticle, in both organisms, formed external to the hypodermis plasma membrane.