The Postembryonic Development of Trichinella spiralis with Special Reference to Ecdysis

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Abstract
Mice inoculated with inective larvae of Trichinella spiralis were killed at 3-hr intervals between the 6th and 17th days of infection. For evidences of molting, larvae from the diaphragm were studied in the living state, in tissue sections, and in solutions of sodium hypochlorite and other chemicals causing swelling of cuticle or shrinking of body tissues. Intestinal worms were recovered from mice at hourly intervals between the 2nd and 46th hr of infection. Prelarvae were found in host muscle on the 6th day, and by the 17th day after inoculation the larvae were resistant to artificial digestion and infective to mice. During this period organo-genesis progressed slowly and gradually; molting was not demonstrated. The overall passiveness and lethargic movement of the larvae throughout the period of differentiation in the muscle appear to be significant in relation to the absence of a molt. During development in the intestine, the larvae were found to molt four times, at approximately 10, 17, 24, and 29 hr in males and at 12, 19, 26, and 36 hr in females. The last three molts in both sexes were preceded by visible alterations in the rectum and sex organs. On a morphological basis, seven distinct developmental stages were recognized: (1) prelarva, produced by parent worm and infective to muscle fiber; (2) tissue-stage larva, with distinct early and late stages in muscle, and when infective to a new host has differentiated to the level of the late third stage of some other nematodes, but lacking ecdysis must be regarded as first-stage larva; (3) five enteric stages, of which the first four molt to become a succeeding stage and the fifth becomes the adult. After the second molt in males, earlier in females, an oval "genital-junction cell" appears between the gonad and reproductive duct. As the latter becomes patent, following the fourth molt, the cell disintegrates.