it can be gathered. A case in point is given by Prof. Herdman. The Mutuvaratu Paar, which lies to the south-west of Karativo Island, yielded during 1889, 1890, and 1891 some 117,000,000 oysters, which realised very nearly 1,000,000 rupees-the only fishery since 1814 that has returned so large a sum. The oysters raised during these three years steadily increased in value, those lifted in 1891-the oldest-being by far the most valuable. "But the record," he remarks, "shows the risk there is in trying for the enhanced value by delaying the fishery once the oysters are over 5 years of age. In 1891 this bed must have been 6 years old, and they are described as rapidly dying off, many being dead and putrid." There are prospects of a good fishing for next year and 1906, but the results of 1907 and the succeeding years depend largely, it is pointed out, on extensive measures of transplantation being undertaken without delay. This Mr. Hornell will doubtless accomplish. Prof. Herdman's memoir on the anatomy of the pearl oyster adds much to our knowledge of the subject, and contains some valuable observations on the living animal. As an instance of the latter we may anchored by the threads of which this is composed. Under a great strain these break, and are renewed again within an hour or so, the root of the old byssus being sloughed off. Some interesting points concerning gill structure are given, especially with regard to the passage from interfilamentar junctions by ciliated discs to junctions by organic union. With regard to sense organs, the pearl oyster is not very well provided. But a distinct response is shown to the stimulus of light and shadow- a sensibility which may be termed dermatoptic," and appears to be located in the edges of the mantle and the surface of the foot, where patches of more or less deeply pigmented epithelial cells are met with. All kinds of creatures seem to find the pearl oyster a particularly "toothsome" morsel, man alone excepted, who prefers to make manure of their bodies for the sake of possible pearls contained therein. No less than seven different kinds of parasitic worms are now known from the pearl oyster, six of which are new species described in this volume. Of these, only a cestode larva (Tetrarhynchus unionifactor), one, FIG. 1.-Pearl-fishing Fleet at work on the Cheval Paar. cite his remarks on the functions of the foot. These, he points out, "are three-fold: the distal ventral surface subserves locomotion; the median and posterior parts effect attachment by means of the byssal fibres; and lastly, on account of the general mobility of the organ, and probably of its sensory nature, the tip is of great use in clearing the gills and mantle from the intrusive particles that cannot otherwise be got rid of." It is concerning the latter function that we would direct special attention here. In the living animal Prof. Herdman has observed the foot "pushed between the gill-plate, and over the inner surface of the mantle gently stroking the surface and insinuating itself into the crevices, thus freeing the parts from any foreign bodies. . . that might cause inconvenience." Mr. Hornell observed one oyster, which had sustained an injury to the mantle, pass the foot-tip gently around the edges of the wound so as to work off the particles of dirt collected there. The tip was even passed through the wound to make the cleansing the more thorough. Concerning the byssus, it is interesting to notice that the operation of dredging for oysters for transplantation in no wise injures the animal when appears to be concerned in the formation of cyst pearls. This fact is interesting, inasmuch as the formation of similar pearls in European mussels is due to the cercaria of trematodes. As to the sequence of hosts called upon to nurse this precious cestode of the pearl oyster to maturity much uncertainty prevails. It was thought that filefishes and elasmobranchs were the intermediate vertebrate hosts, and this will probably prove to be the case. Certain novel features seem to be foreshadowed in the life-history of this parasite when the chain of evidence is complete. To begin with, it would appear that it enters its first host-the pearl oyster -as a free-swimming planaria-like larva, inasmuch as certain larvæ of this type, but containing calcareous corpuscles recalling those of cestodes, were taken in plankton, and these bear, in many features, a close resemblance to the earliest encysted larvæ found in the pearl oyster. It is assumed that these free-swimming forms are tetrarhynchids, though hitherto it has been believed that tetrarhynchid larvæ make their way into their first hosts while still encased within the egg-shell. The bothriocephalids have free-swimming larvæ, but these are ciliated. That the larvæ in question must be tetrarhynchids seems certain, since older larvæ, showing several stages of development, belonged unquestionably to the genus Tetrarhynchus. It was believed that these larvæ were next ingested by file-fishes (Balistes), but it now appears that the tetrarhynchid larvæ of Balistes, of which three species are described in this report, are quite distinct forms. distinguished by the presence of a vesicle, which is wanting in the pearl oyster larvæ. Further, the more advanced larvæ of the pearl oyster have arrived at a later stage of development than the larvæ found in Balistes. THE VERY LATEST "TYPE" OF EXTENSIMETER IS, THE "O'TOOLE." A Simple, Convenient, Accurate, and Reliable Instrument, designed by the Rev. Father O'Toole, for Students' use in determining the coefficients of expansion of metal rods, at a moderate price. 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