November 18, 1922J 



NA TURE 



667 



in metaphors ; they evidently have something quite 

 definite before them which they believe is conveyed 

 to their readers. Is it what other writers, e.g. Sir 

 Frederick Mott, would call innervation ? Apparently 

 so, for he writes in ' ' The Brain and the Voice in Speech 

 and Song " {Harper's, 1910) of " innervation currents." 

 Now currents must be real, must be a flowing of 

 something. 



Clinicians — neurologists — believe in nerve energy, 

 but apparently they do not derive their belief from 

 their physiological teachers, for, according to 

 McDougall, " the professional physiologists refer to 

 it (nerve energy) contemptuously as a survival from 

 the Dark Ages." Without doubt, something here 

 is in need of being cleared up. 



The intelligent layman thinks there is such a thing 

 as " nerve energy," physicians use the term con- 

 stantly, some professional physiologists use it when 

 they find it convenient, and yet Dr. Adrian assures 

 us that "as a physiological concept, 'nerve energy' 

 has little to recommend it." If that is so, it is un- 

 fortunate the term is so popular. Dr. Adrian, 

 however, concedes that " If the term 'nerve energy' 

 is to be retained, it might be used to mean the total 

 potential energy in the neurone available for use in 

 the transmission of impulses." 



This definition is so broad that it would cover (as 

 it should) such cases of innervation as cerebellar 

 control of other nerve centres, as well as unconscious 

 cerebral inhibition of certain lower centres, neither 

 of which could be called mental energy. 



This is all that is wanted as a beginning of the 

 clearing of the air. In this sense, nerve energy is 

 real. I had only suggested it might be measured 

 in order, if possible, to satisfy the demand that as 

 a form of energy it should be measured. 



It now remains for some physiologist to discuss 

 the reality of nerve energy by defining the concept, 

 relating it to nerve impulses and to innervation- 

 processes, and placing the term in his index. Then 

 the neurologist and psychopathologist would know 

 whether he was using the term nerve energy in the 

 same sense as that in which other men of science 

 use it. In time, something more definite than at 

 present would filter through to the laity. 



D. Fraser Harris. 



Dalhousie University, Halifax, N.S., 

 October II. 



Habits of Echinus esculentus. 



In the October issue of the Journal of the Marine 

 Biological Association, Miss Trewavas records the 

 occurrence of Echinus esculentus between tide-marks 

 on the Cornish coast and makes a request for informa- 

 tion " of the occurrence or absence of this sea-urchin 

 between tide-marks at other parts of the British 

 coast." 



In this district E. esculentus occurs abundantly 

 between tide-marks in spring and early summer, on 

 rocky coasts ; a few may be found at almost any 

 other season. About February or early March a 

 shoreward migration seems to set in, so that in suitable 

 weather conditions some hundreds may be collected 

 at springs between April and June. Then their 

 abundance decreases until about November, from 

 when until January it is at a minimum. This inshore 

 vernal maximum is coincident with the spawning 

 season ; ripe individuals being found from February 

 to August with a maximum occurring in early May. 

 A similar shoreward spawning migration occurs in 

 other, chiefly Boreal, species — Solaster papposus, 

 S. endeca, Henricia sanguinolenta, Archidoris tubercu- 

 lala, Jorunna Johnstoni, Aeolidia papulosa, Leander 



NO. 276S, VOL. I 10] 



squilla, Spironiocaris pusiola, and doubtless various 

 other species. 



The presence of E. esculentus between tide-marks 

 is strongly influenced by various conditions — e.g. 

 (1) in April 1 921 a spell of sharp frosts caused numerous 

 urchins which had invaded the intertidal zone to 

 retire to deeper water, where they were visible in 

 abundance in 1-2 fms. ; (2) during the hot spell of 

 May and June 192 1 they were unusually scarce 

 between tide-marks ; (3) in April 1922 a spell of 

 heavy weather either washed away or caused a 

 temporary seaward movement of urchins from the 

 intertidal area, and further, although they had also 

 been abundant in 1-2 fms., none were to be seen 

 there, all having apparently retired into the shelter 

 of crevices and boulders. There is some evidence 

 that males approach the shore ahead of the females. 

 While inshore, urchins feed very largely on barnacles. 



On an average the life of E. esculentus, as an 

 urchin, begins about midsummer : the first months 

 are spent in the Laminarian zone browsing freely on 

 such limy food as Membranipora ; by the end of the 

 calendar year some are well over 2 cms. in diameter 

 and at the close of their I. -year period about 4 cms., 

 the more advanced having spawned about May at 

 an approximate age of 10-12 months. The 1 1. -year 

 group appear to range between 4-7 cms., the III. -year 

 group 7-9 cms., and the IV. -year group 9-1 1 cms. 

 Largely owing to the prolonged spawning period 

 there is no discontinuity between the year groups, 

 which merge into one another. The adults feed 

 on Polyzoa, Laminaria — particularly if encrusted with 

 Membranipora, — balanids, etc. In October urchins 

 are found with large gonads rich in fats ; an occasional 

 one may have a few immature ova. The yearly 

 cycle would seem to be : 



July-November — Growth and fattening of gonads — ■ 

 Laminarian zone offshore. 



December-March — Maturation of gonads — Laminarian 

 zone offshore. 



April- June — Spawning — largely inshore. 



Richard Elmhirst. 

 Marine Biological Station, 

 Millport. 



Perseid Meteors in July 1592. 



May I bring it briefly to the notice of readers of 

 Nature that there is apparently a reference in the 

 history of Akbar, the Emperor of India, to a brilliant 

 display of Perseid meteors in the Panjab about the 

 end of July 1592. The passage occurs in the account 

 of the 37th year of the reign, and just before the 

 description of Akbar's expedition to Cashmere. 



Akbar and his son Daniel had left Lahore and 

 crossed the Ravi, and were encamped at a garden 

 called the Rambari. On the 27th day of Tir O.S., 

 which might correspond to about July 28, 1592, 

 three hundred little stars or pieces of stars (sitdracha) 

 were seen traversing the heavens from west to east. 

 The Persian text does not say whether this was in 

 the day or in the night, but presumably it was the 

 night or at least the evening, for the meteors would 

 not be visible during the day. 



Akbar and his son were so alarmed at this appear- 

 ance, which took place three days after their departure 

 from Lahore, and while they were still encamped 

 at Rambari, that they at once consulted the astrologers 

 who were with them in the camp and by their advice 

 broke up their camp and returned to Lahore. Nor 

 did they resume their march till about a fortnight 

 later and after the}-' had ascertained a more auspicious 

 day for a start. 



