Larvae were placed on a microscope slide with a raised cover slip. The first 100 larvae encountered were rated into seven and eight developmental categories, respectively (Table 2.2 and Table 2.3). The first ten normal larvae encountered were measured using an ocular micrometer (body length, BL, and postoral arm length, PO,for E. chloroticus, Table 2.2; shell length for H. iris, Table 2.3). In one E. chloroticus assay, larval size was determined by taking a photo of each larva using a different microscope than in the previous assays, and measuring BL and PO using the image software Image J. In order to remove any bias due to the difference in methodology,only the PO/BL ratio was used in subsequent analyses.