. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MIGRATORY HABITS OF LIMNORIA 63 broods; Station B, mid-February-mid-May, 1953 (mean temperature ° C.) two broods. Using size as a criterion, it appears that migrant females may have produced one or two broods prior to migration. This is indicated in Figure 3 which should be coordinated with Table II showing that females may become gravid in size class 6. Females in size class 10, the largest, were found only in migrant populations. Although migrants must frequently land on already heavily infested wood, the relative abse
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MIGRATORY HABITS OF LIMNORIA 63 broods; Station B, mid-February-mid-May, 1953 (mean temperature ° C.) two broods. Using size as a criterion, it appears that migrant females may have produced one or two broods prior to migration. This is indicated in Figure 3 which should be coordinated with Table II showing that females may become gravid in size class 6. Females in size class 10, the largest, were found only in migrant populations. Although migrants must frequently land on already heavily infested wood, the relative absence of the large females probably indicates that few, if any, re-establish themselves in dense populations. Thus the implication is that migra- tion is largely an urge to seek less crowded conditions. Analysis of the population forming the basis of Figure 3 shows also that the summer and fall gravid migrants 50 40 PILING MIGRANT 203 ANIMALS 390 tr UJ Q_. 10- 0- AVERAGE WIDTH IN MILLIMETERS FIGURE 3. Limnoria tripunctata. Percentage size composition of gravid female populations. average mm. smaller than those of other seasons and the gravid females from piling average mm. smaller, thus indicating that sexual maturity is reached at a smaller size (hence more rapidly) during the warmer months. That reproduction in Limnoria is influenced seasonally by temperature is further indicated by a study of the "gravidity" which may be denned as the per cent of gravid females among the adult females occurring at any time in a piling popu- lation of maximum density (Table VII). From Table VII, it seems evident that gravidity for this species reaches its peak somewhere between 17° and 19° C., declining at temperatures above and below these values. Gravidity appears to double between 14° and 18° C. In laboratory cultures only 28% became gravid at 24° C. The broods of specimens kept at 34° C. deteriorated, suggesting that such high te
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