248 



NATURE 



[July 14, 1887 



the parietal eye, like the animal in which it occurs, reverts 

 towards an ancestral condition, and its doing so is an 

 additional point in favour of Dohrn's opinion that the 

 change to the adult Petromyzon is a sort of atavism. 



Myxine, though in other respects more degenerate 

 than the adult Petromyzon, retains the structure of the 

 retina in a somewhat . more specialized condition, one 

 which most nearly recalls the highest parietal eye pre- 

 sented to us by the Lacertilia. 



With regard to the development of the eye in lizards, 

 the only point I will now mention is one which was 

 to be expected to hold, viz. that the lens develops as a 

 thickening of the anterior wall of the vesicle. I may 

 add, however, that it shows signs of a tendency to 

 involution. 



And now, without discussing Spencer's speculations, I 

 will briefly state my idea of the manner in which the 

 parietal eye was evolved in connexion with the paired 

 eyes. 



From the start of my investigations I was fully con- 

 vinced that the evolution of all three eyes must be viewed 

 from one common starting-point. The fact that, as 

 Wiedersheim states, even in man nerve-fibres have been 

 traced from the optic thalami to the pineal gland, is suffi- 

 cient evidence for this, even if we did not know that all 

 three eyes arise in connexion with the same portion of 

 the brain. The hypothesis is an extension of that given 

 by Wiedersheim, Carriere, Dohrn, and others, to account 

 for the evolution of the paired eyes. 



The starting-point is a dorsal optic plate before the 

 neural folds begin to form. This gives us a dorsal eye on 

 the so-called invertebrate type. When the neural folds 

 began to form so as to involute the brain and spinal cord, 

 the optic plate was of course, being part of the brain, 

 involved in the involution. With the progression of the 

 latter it probably increased in size, and extended some- 

 what over the lateral margins of the neural folds. 



When the neural folds closed and shut in that which 

 forms the optic vesicles, part of the optic plate was left, 

 forming the rudiment of the parietal eye. This, just as 

 all known sense-organs tend to get involuted, got also 

 secondarily involuted, and that but slowly, so that the 

 outside wall of the involution had time to become a lens, 

 an eye being thus formed on the invertebrate type. The 

 parietal eye, being closely bound up with the paired 

 eyes, got secondarily involuted with them ; and, losing 

 its primary mode of origin by delay in its development, 

 it now appears as a secondary outgrowth of the brain, in 

 which the lens is still formed from the outer wall. The 

 lens, moreover, possibly retains traces of an involution. 



Spencer has not attempted to grapple with the difficulty 

 involved in the fact that the rods of the retina of the 

 paired eyes are turned from the source of light, while in 

 the parietal eye they are turned towards it. 



The explanation given above is not in contradiction 

 with this state of things ; it, in fact, receives support 

 from it. 



In the complete paper I shall discuss the matter at 

 length, and give ample illustrative figures. 



J. Beard. 



Anatomisches Institut, Freiburg i/Br., June 21. 



THE JUBILEE ANTICYCLONE. 



" /QUEEN'S WEATHER" has long been a famihar 

 \^ expression descriptive of the most desired weather 

 for all open-air celebrations and enjoyments ; and per- 

 haps no June of the last fifty years has presented us with 

 so many days of such choice weather as the June of 1887. 

 In the language of modern meteorology this is due to the 

 fact that the prevailing type of weather has been anti- 

 cyclonic. From the middle of June to the beginning of 

 July, thus including the time of Her Majesty's Jubilee, a 



very pronounced and remarkable anticyclone overspread 

 the British Islands, with its usual attendants of bright 

 weather, strong sunshine and heat during the day, clear 

 and cool nights, and capriciously- distributed rainfall. 



Taking June as a whole, temperature was most 

 in excess of the average in the west and north-west 

 of Ireland and over Central Scotland from Inverness 

 to the Solway ; the excess at Glencarron, in Ross-shire, 

 being 5°'o, at Laing and Braemar 4°-5, and in many places 

 in Scotland and the west of Ireland about 4°*o. The 

 exceptional character of these temperatures will appear 

 from the fact that during the present century they have 

 only been exceeded in the north-east of Scotland in the 

 Junes of 1 818, 1826, and 1846. On the other hand, over 

 England, to the east of a line drawn from Berwick to the 

 Isle of Wight, and to the north of a line from Stornoway 

 to Wick, temperature does not appear to have exceeded 

 the mean of June more than a degree : whilst at Somer- 

 leyton in Suffolk, and North Unst in Shetland, the tem- 

 perature fell fully a degree below the average. These 

 differences were due to the general position of the centre 

 of the anticyclone being well to westward of the British 

 Islands, so that the northern islands and the south- 

 east of England were within the eastern margin of 

 the anticyclone, and hence exposed to the northerly 

 winds and lower temperatures peculiar to that sec- 

 tion of an anticyclone, as was pointed out in 

 Nature ten years ago in reviewing the American Weather 

 Maps. During this anticyclonic weather there were two 

 distinct sources of high temperature, viz. that due to the 

 strong sunshine which found its most decided expression 

 in the high temperatures of Central Scotland ; and that 

 due to the warm descending air-currents of the anti- 

 cyclone, which being most marked at great heights was 

 most strongly expressed at the Ben Nevis Observatory. 

 At this Observatory the means, for the ten days ended 

 June 26, of the daily maxima were 6i°'8, and of the 

 minima 5o°'3, thus giving a mean temperature of 56°'o, 

 and ii°'5 for the daily range. Quite different was the 

 temperature during these ten days at low levels inland. 

 At Pinmore, for example, in the deep valley of the 

 Stinchar, Ayrshire, the mean temperature was 63'''4, and 

 the daily range 33°"3, or three times greater than on the 

 top of Ben Nevis. On June 21 the contrast was very 

 striking, the minimum on Ben Nevis being 43°'o, 

 whereas at Pinmore it fell to 34°'3, on which 

 morning, as reported by Mr. Donald, the ob- 

 server, it was freezing at the river side. During the 

 night the high temperature was kept up on Ben Nevis 

 by the descending air-currents of the anticyclone, but 

 the cold currents generated by the night radiation con- 

 centrated on and filled the steep narrow valley of the 

 Stinchar. 



The frequent occurrence of 40° o and upwards between 

 the daily maximum and minimum, so frequently observed 

 over the country, was primarily dependent on the clear dry 

 atmosphere and the strong solar and terrestrial radiation 

 consequent thereon. These great and sudden changes 

 of temperature were on occasions largely increased by 

 the shiftings of the position of the anticyclone, by which 

 a particular locality was at one time on its west side, and 

 therefore in enjoyment of the high temperature peculiar 

 to that position, but a few hours thereafter was within its 

 eastern side and its low temperature. 



So far as records have reached us, the rainfall was 

 nowhere above its average, being, however, at or close to 

 the average at Glenquoich and Glencarron, where it was 

 respectively 5'53 and 4"i9 inches. On Ben Nevis 7'5i 

 inches fell, being only o"66 inch less than the average. At 

 Oxford, the deficiency from the monthly mean was only 

 15 per cent, and at Somerleyton 23 per cent. Generally, 

 however, the deficiency was exceptionally great and wide- 

 spread, being in nearly all parts of the British Islands 

 from 50 to 95 per cent, less than the June average of the 



