Nov. 14, 1889] 



NATURE 



31 



called by the villagers, will not sufTer the like fate. The Italian 

 Alpine Club, will, we may trust, interest themselves ia this 

 matter. P. L. Sclater. 



Hotel du Pare, Lugano, October 21. 



Who discovered the Teeth in Ornithorhynchus .' 



As Dr. Hart Merriam's letter on the above subject in your 

 issue of the 7th inst. (p. 11) will be read by many who have not 

 access to Sir Everard Home's " Lectures on Comparative 

 Anatomy," allow me to point out that the description and figures 

 in that work referred to by Dr. Merriam have no bearing whatever 

 upon the very interesting discoveries recently made. They 

 represent, not the real teeth of the young animal discovered by 

 Mr. Poulton, and fully described by Mr. Oldfield Thomas, but 

 the well-known horny plates which functionally take their place 

 in the adult, and which are called "grinding teeth" by Sir 

 Everard only in a very general sense. W. H. Flower, 



British Museum (Natural History), November 9. 



The account of the teeth of Ornithorhynchus, given by Sir 

 Everard Home in "Lectures on Comparative Anatomy," vol. i. 

 p, 305, explanatory of Tab. lix. vol. ii., referred to by Mr. Hart 

 Merriam in your last issue (p. 11), shows, even more clearly 

 than the figures, that the true teeth had not been noticed at that 

 time (1814). The passage is as follows: — "In the posterior 

 portion of the mouth, both in the upper and lower jaw, are 

 placed grinding teeth with broad flattened crowns, four in num- 

 ber, one on each side of each jaw. They art composed of a horny 

 substance (the italics are my own), only embedded in the gum, 

 to which they are connected by an irregular surface in the place 

 of fangs. When cut through, the substance appears fibrous, 

 like that of nail ; the direction of the fibres being perpendicular 

 to the crown, similar to that of the horny crust of the gizzard. 

 The teeth in the young animal are smaller, and two on each 

 side, so that the first teeth are probably shed, and the two small 

 ones replaced by one large one." 



It is perfectly evident that here no reference is made to the 

 trite teeth, and, moreover, the figure of the two smaller "teeth " 

 of young specimens represents merely the immature horny 

 plates. The honours, therefore, still remain with Mr. Poulton 

 and Mr. Oldfield Thomas. Oswald H. Latter. 



Anatomical Department, The Museum, Oxford, 

 November 8. 



On a Mite of the Genus Tetranychus found infesting 

 Lime-trees in the Leicester Museum Grounds. 



About the 13th of last September my attention was called to 

 the strange appearance of a row of lime-trees .standing in front 

 of the School of Art buildings in Hastings Street. On examina- 

 tion I found that the whole row, with, I think, only one excep- 

 tion, were almost entirely devoid of leaves, the trunks and 

 branches being covered with a fine web, very closely spun, 

 giving them the appearance of being coated with a thin layer of 

 ice, this glazed look being specially noticeable when standing in 

 such a position as to catch the reflected rays of the sun. At first 

 sight I imagined that I was examining the work of a spider, 

 though I was unable to recollect any whose webs would accord 

 with the character of those under observation. However, a 

 close inspection revealed the webs to be tenanted by an in- 

 numerable number of yellowish or orange-coloured mites which 

 were in some places associated together in dense masses or 

 clusters, and more or less abundant over the whole of the trunks 

 and branches. 



These mites appeared, on being subjected to a careful 

 microscopical examination, to be identical with Tetranychus 

 tiliariim. Mull., a species which it seems that Claparede con- 

 siders to be only a variety of T. telaritis, the common "red 

 spider." However that may be, they are at any rate closely 

 allied forms — members of the family Trombidiida:, which pos- 

 sess, as one of their distinguishing characteristics, a pedipalpus 

 with a claw and a lobe-like appendage. In the genus 

 Tetranychus the palpi are chelate, the mouth is furnished with a 

 barbed sucking apparatus for the extraction of plant juices, and 

 spinning organs are usually present. It is needless to comment 

 upon their destructiveness to vegetation, for most keepers of 

 gardens and hothouses are familiar with their ravages in one 



direction or another, and the difficulty experienced in thoroughly 

 extirpating them. 



In connection with the species which forms the subject of the 

 present communication, I notice that Murray, in his work on 

 the " Apt era," says : "It occasionally occurs in such numbers 

 as almost to denude the trees of their foliage ; and it has been 

 noted that the stems and branches of such trees feemed covered 

 with a bright glaze. Can this be a fine web ? " It was so, most 

 certainly, in the present instance, which afforded me a most 

 favourable opportunity for examination. Again, it appears that 

 the mites are normally found on the under-surface of the leaves, 

 which they cover with a fine web of silk, on which (to again 

 quote Murray) "they are sometimes crowded together in vast 

 numbers ; for example, we have seen them so thick on the leaves 

 that they looked as if they were not merely sprinkled with a yellow 

 orange coloured powder, but as if it was actually in parts heaped 

 up on them, so that none of the green colour of the leaf was visible." 

 Their presence is of course highly injurious, causing the leaves 

 to shrivel and drop ; and it seems to me that the fact of their 

 occurrence on the bare bark of the trunks was attributable to the 

 death of the leaves causing them to retreat to that position, 

 uncongenial though it would seem to be. Such trees as pre- 

 served their foliage presented no abnormal appearance on the 

 branches, &c., notwithstanding which, in one or two instances, 

 I believe the parasites were present on the leaves, though seem- 

 ingly not in such extraordinary profusion. 



Duges, writing of 7'. telaritis, states his belief that that species 

 passes the winter under .stones, and instances the finding of 

 several active individuals so situated in a garden near Paris in 

 the month of October. Regarding this point I may say that my 

 specimens of T. tiliarum, which I placed in a box immediately 

 after removal from the trees, speedily ensconced themselves 

 in the most convenient nooks and crannies, in which they spun 

 fine webs. It may be worth noting that the days on which my 

 observations were made were warm and damp, with scarcely 

 any wind, quite typical early autumn days in fact. 



F. R. Rowley. 



Leicester Museum. 



Retarded Germination. 



I shall be much obliged to any of your readers who can give 

 an explanation of the probable cause of the above phenomenon, 

 which I have remarked this year. I sowed a number of patches 

 of seeds of various hardy annuals in the garden in the last week 

 of April ; about half of them came up after the usual interval, 

 strongly and regularly. Such were Calendula Pongei, Con- 

 volvulus minor, Lavatera iriniestris, Collinsia bicolor, Ibens 

 white and red, Specularia speculum, Linum rubrum, &c., &c. 

 Then there were some of which a few scattered seedlings made 

 their appearance at this time, and after an interval of about six 

 weeks the greater part of them also came up ; among these were 

 Eiitoca viscida, Nigdla damasccna, Sphenogyne, and Clarkia 

 pulchella. Thirdly, there were some of which I quite despaired ; 

 mignonette, however, appeared thinly about the end of June, 

 and at intervals till August ; and in the middle of June a few 

 plants (in proportion to the seed sown, a few) of Linaria bipartita. 

 Madia elegans, and Xerantheinum came up — one consequence 

 being that the last named has not yet flowered. Some of the 

 seeds were obtained this spring from seedsmen, some were my 

 own collection of the last year or two — of the latter were 

 Calendula, Lavatera, Convolvulus, Specularia, Eutoca, Ni^ella, 

 Sphenogyne, and mignonette — so that cannot be said to give any 

 clue. The conditions for germination and growth were favour- 

 able, and the season also. I have never remarked before any 

 annuals so long in appearing above ground ; though in some 

 herbaceous plants I have noticed it, e.g. Gaillardia, Myosotis 

 alpestris, and Anemone coronaria. E. A. 



Herefordshire, September 19. 



The Relation of the Soil to Tropical Diseases. 



As a humble subscriber to and student of Nature, will you 

 bear with me while I ask your help, as shortly and plainly as I 

 can ? I am in a very secluded corner of one of the Native States 

 of Rajpootana, and I am collecting facts and making observa- 

 tions on the relation of the jmV to tropical diseases ; my ambition 

 being to discuss it not so much from a statistical and geographical 

 standpoint, as from the geological, in its chemical and biological 



