The following paragraphs give a brief comparison of our findings with two recent test experiments on fouling and growth, one from the Northern Hemisphere page 14 and one from the Southern. Corlett (1948) describes observations in the Mersey Estuary during 1946 and 1947, using tiles and scallop shells as test units. It should be noted that surface, texture, size, and the time period for immersion differed in our and Corlett's experiments, but the same groups of organisms set in both. However, the most conspicuous groups in Corlett's investigation were not the same as in the present instance. Hydroids, barnacles, and mussels were the most important settling organisms with Corlett, while species of polyzoa, ascidians, and hydroids in that order were dominant organisms in Port Nicholson. The hydroids are important in both investigations. Otherwise, the groups that were most important in the Mersey Estuary were some of the least important in the present experiment. In most groups, a greater number of different species settled in the Northern Hemisphere—e.g., five species of barnacle as against a single species in Port Nicholson. This was also the case with the Australian investigation when compared with our New Zealand tests, and may probably be explained by the fact that in the present experiment the test blocks were confined to one situation of limited area, whereas Corlett, and Allen and Ferguson Wood, had several stations with varying conditions and at points some distance from each other. Species of the genera Tubularia, Mytilus, and Enteromorpha showed in Corlett's and our tests, while the ascidian B. schlosseri set at approximately the same season in both hemispheres—namely, early autumn in England and late autumn in New Zealand B. schlosseri was not, however, as prominent a species in Corlett's experiment as it was in ours.

Tests carried out in Australia by Allen and Ferguson Wood (1950) are more comparable with our experiment than are Corlett's, as approximately the same time elapsed (30 and 28 days respectively) between the raising of each test block. Also, Allen and Ferguson Wood had long-term units down for three and six months to obtain succession and rates of growth, and short-term units down for seven to fourteen days. The Australian workers, however, used glass plates for test units, thereby obtaining a more rapid check on the settling organisms than could be obtained from the wooden blocks. Their test units were suspended one to two feet below low-tide level, as against our four feet. The following genera, Ectocarpus, Enteromorpha, Ceramium, Mytilus, Sycon, Spirorbis, and the species, Obelia australis, Bugula neritina, and Galeolaria hystrix, were present in both experiments. None of the species of ascidians recorded by Allen and Ferguson Wood was found in the present study.