Observations on the Larval Stages of Muellerius capillaris within the Intermediate Hosts Agriolimax agrestis and A. reticulatus

The rate of development of the larvae of M. capillaris is slowed down as the temperature is lowered; at 25°C. the infective stage is reached after 8 days; at 5°C. after 98 days. 2. The differences between “pre-infective” and “infective” larvae, as described by Gerichter (1948), have been confirmed. 3. Larvae at the “infective” stage can withstand artificial digestion, but “pre-infective” larvae are unable to do so. 4. The infective larvae can survive for long periods within the foot of the intermediate host. 5. Pre-infective larvae can survive for seven days after the death of the intermediate host; infective larvae can live for sixteen days. 6. Naturally-infected slugs were found throughout the greater part of the year. 13.5 per cent of the slugs collected were infected but in most instances only a few larvae were present in any one slug.