i 3 2 BIOLOGY AND ZOOLOGY 



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volumes containing over 700 pages, 428 figures and 76 plates* This memoir is in the 

 first place systematic, but it contains many discussions of morphological, physiological 

 and embryological points, and a very full list of reference to literature. The author 

 insists that the medusa form has been acquired independently in different groups. 

 F. Wood Jones has published an interesting contribution to the theory of coral-reef 

 formation (see E. B. vii, 132 et seq.), the result of observations made during a pro- 

 longed residence on the Cocos-Keeling atoll. He thinks that Darwin's subsidence 

 theory cannot explain the formation of this atoll, for the lagoon has become shallower 

 since 1825, and the structure of the reef shows no evidence of subsidence since its 

 first formation. Equally he rejects Murray's theory of solution, as coral sand is 

 constantly accumulating in. the lagoon and calcium carbonate is being deposited. He 

 thinks that the process of sedimentation is the chief factor. Corals are unable to grow 

 where sediment falls on the zooids in any quantity, and accordingly the set of winds 

 and waves and the limit of the slope on which sediment will lie quietly are the defining 

 conditions of coral growth. Where there is a free wash of water, the zooids are kept 

 clear of sediment and flourish; where there is an eddy or a quiet pool, or a depth of water 

 beyond the reach of the waves, sediment lies and inhibits coral growth. 



Echinoderma. 



. The most important new work on the group (see E. B. viii, 871 et seq.) is Mr. H. L. 

 Hawkins' memoir on the Holectypoid sea-urchins, which he regards as forming an 

 order intermediate between the regular and irregular urchins, but which have been 

 characterised by a " persistently retarded progress in evolution," with the result that 

 study of them throws much light on the relations and classification of the whole group. 



Pearl Oysters. 



Dr. Lyster Jamieson has published several memoirs dealing with the pearl-fishing 

 industry in different parts of the world (see E. B. xxi, 25 et seq.), and the practical 

 failure of attempts that have been made to improve it by biological investigations, 

 a failure which he is disposed to attribute in the first place to the inexperience of the 

 investigators with the practical side of the industry. In particular he throws doubt 

 on an interesting theory which seemed to have a practical bearing. The pearly sub- 

 stance is frequently deposited round some adventitious foreign body which has found 

 its way to the pearl oyster. In the case of the Ceylon pearl oyster, the foreign body 

 was supposed to be the larva of a tape-v/orm, the adult stage of which infests a fish 

 which preys on the oysters. It seemed a possible inference that if the fish were en- 

 couraged near the oyster beds, there would be a greater chance of oysters being infected 

 by the eggs of the tape-worm, with a consequent increased production of pearls. Dr. 

 Jamieson's observations lead him to dispute the fact and the inference. He thinks it 

 more probable that the production of pearls in the oyster is the result of a pathological 

 immigration of the epidermis into the tissues, the cause of which is unknown, and that 

 if tape- worm larvae do really occur in the shell-fish, the case is one merely of the co- 

 incident presence of two diseases, one associated with pearl-production and the other 

 with no practical relation to it. 



Disease- Bearing Arthropods. 



The new knowledge of the part played by biting and blood-sucking Arthropods 

 in the carrying of disease from infected animals to man, from man to man, or from 

 man to animals, has led to much careful work on the Arthropods themselves (see E. B. 

 ii, 673 et seq.). Of this the most important are a great monograph on ticks (Ixodoidea) 

 by Messrs. Nuttall, Warburton, Cooper and Robinson; the fifth and completing volurne 

 of Theobald's monograph on the Culicidae, in which there are invaluable descriptions 

 of tropical gnats and mosquitoes; and E. E. Austen's beautifully illustrated treatise 

 on African blood-sucking flies. On the practical side, there has been an increasing trend 

 of opinion towards incriminating large game animals, especially in Africa, as permanent 

 reservoirs of disease, with the consequent demand for the relaxation or abolition of the 



