344 



NA TURE 



[September 9, 1922 



Mr. H. P. Sherwood, assistant naturalist to the 

 Ministry, may be of interest. 



Experiments in oyster culture in tanks are being 

 carried out by the Ministry at Conway on a large 

 . scale, and have been in progress for several years. 

 In order to throw light on the frequent failure of spat 

 settlement under natural conditions, and the remark- 

 able success which has almost uniformly attended the 

 breeding experiments in the Conway tanks, special 

 attention has been directed to the identification of 

 enemies of the embryo oyster. Some six weeks ago 

 large numbers of Noctiluca miliaris were noted in the 

 Conway estuary, which has since contained this 

 organism in varying quantity. Laboratory experi- 

 ments were carried out, and Mr. Sherwood noted a 

 remarkable and rapid diminution in the numbers of 

 oyster embryos placed in aquaria in the presence of 

 Noctiluca. He afterwards found that many of the 

 Noctilucas contained from one to four oyster embryos. 

 The embryos were seen at the outset in, or in close 

 proximity to, the peristome and mouth, later becoming 

 scattered through the substance of the Noctiluca, 

 enclosed in distinct food vacuoles. 



Mr. Sherwood has made a long series of confirmatory 

 observations, and the actual ingestion of the embryos 

 has now been repeatedly observed, including the 

 transference of the embryo to parts remote from the 

 mouth. 



Many exceedingly interesting observations with 

 regard to the mechanism of ingestion, etc., have been 

 made, but a full description would be out of place in 

 a short communication. It may, however, be noted 

 that the tentacle of Noctiluca appears to take no 

 active part in the process of ingestion. The behaviour 

 of the embryos suggests that their movements, and 

 therefore power of escape, are inhibited after contact 

 with the oral groove, either by entanglement of the 

 cilia with mucus, or by actual paralysis induced by 

 the action of some " stinging " mechanism. Further 

 investigation is required, however, before any definite 

 deductions can be drawn. 



When it is considered that Noctiluca often occurs 

 in the sea in enormous numbers, and that each 

 Noctiluca can dispose of at least as many as four 

 oyster embryos at a time, the importance of this 

 observation will be apparent. I am informed that 

 great quantities of Noctiluca have recently been 

 observed in the vicinity of the oyster beds at Orford. 



Another observation recently" made by Mr. Sher- 

 wood, in connexion with the disappearance of oyster 

 spat, is of interest. Not only has he found oyster 

 embryos in the stomachs of adult oysters, but also has 

 found the stomach of a " black sick " oyster, taken 

 from a tank in which there was no free-swimming spat, 

 crammed with embryos in the same stage of develop- 

 ment as those found in the gills of the parent oyster. 

 It would thus appear that the oyster is not only a 

 cannibal, but also even devours its own young before 

 extrusion. 



The very interesting observations made by Dr. 

 J. H. Orton (Nature, August 5, p. 178) on the 

 ingestion of oyster embryos by Aurelia aurita throw 

 further important light on the question of failure of 

 oyster spat fall. R. W. Dodgson. 



Ministry of Agriculture and Fisheries, 



Fisheries Experiment Station, 



Castle Bank, Conway, August 18. 



Defoliation of Oaks. 



In view of the deplorable effect of repeated defolia- 

 tion of oaks by the larva? of Tortrix viridana, as noted 

 by Mr. E. W. Swanton in Nature for August 19, 

 p. 250, it may be useful to remind planters that there 



NO. 2758, VOL. I io] 



are two distinct races of British oak (Quercus robur, 

 Linn.), to which some botanists have assigned specific 

 rank as Q. pedunculata, Ehrh., and Q. sessiliflora, 

 Salisb. The latter, known in the vernacular as the 

 durmast oak, prevails as an indigenous growth in the 

 western and north-western parts of Great Britain, 

 throughout the English Lake District, and in Ireland. 

 In eastern England and Scotland and in midland and 

 southern England the pedunculate oak predominates, 

 but not exclusively, for I have found that the old trees 

 in Merevale Park, Warwickshire, survivors of the 

 ancient Forest of Arden, are durmast, while such oaks 

 as have been planted there are pedunculate. 



The timber of these two varieties (or species) are 

 of equal quality, the durmast being of straighter 

 growth than the other; but there is an important 

 and well-marked difference in their relative suscepti- 

 bility to the ravages of Tortrix. The Hon. Gerald 

 Lascelles, late deputy surveyor of the New Forest, 

 directed my attention to this many years ago. " I 

 have seen," he said, " a sessile oak standing out in 

 brilliant foliage when every other oak in the wood 

 around was as bare of leaf as in winter." 



Subsequent careful observation in all parts of the 

 country has fully confirmed Mr. Lascelles's statement. 

 Unfortunately, the durmast forms and ripens acorns 

 far less frequently than the pedunculate oak ; hence 

 the difficulty of obtaining durmast seedlings and 

 plants from nurserymen, and the vast preponderance 

 of the pedunculate oak in British and Irish plantations. 

 Herbert Maxwell. 



Monreith, Whauphill, 

 Wigtownshire, N.B. 



Black Coral. 



Prof. Hickson, in his interesting article on Black 

 Coral (Nature, August 12, p. 217), alludes to the 

 remains of Noah's Ark as quoted by Josephus from 

 Berosus and others. It is said in Josephus (he. cit.) 

 that " the remains of the timber were a great while 

 preserved." There is in the Monastery at Etch- 

 miadzin a small piece of Noah's Ark carefully framed. 

 It was given by an angel to a monk named James, 

 who had wandered on Ararat in search of it for seven 

 years (see J. B. Telfer, " The Crimea, etc.," 1876, 

 p. 250). So far as I could see, when I examined it 

 in 1898, it was neither wood nor fossil wood, but 

 asbestos. This does not render improbable the 

 occurrence of bitumen in the neighbourhood, but why 

 does Prof. Hickson assume that the amulets were 

 bracelets ? In default of evidence that Noah utilised 

 the Ark for dredging, there does not seem any reason 

 to connect him with black coral. 



F. A. Bather. 



Metallic Coloration of Chrysalids. 



In Nature of November 3, 1921 (vol. 108, 

 p. 302), a letter of mine appeared on the " Metallic 

 Coloration of Chrysalids." During the present year 

 I have had the opportunity of observing some very 

 fine examples of the chrysalids of R. utticcs, in which 

 the gilding extended over the whole surface. It may 

 be of interest, as bearing on the origin of the colour, 

 to note that w-hen the gilding was very gently scraped, 

 the gold first turned to green and then to blue. In the 

 course of a few days the scraped area assumed the 

 same appearance as the whole chrysalid does after the 

 butterfly has emerged, namely, a yellowish white. 



A. Mallock. 



9 Baring Crescent, Exeter, Aug. 24. 



