238 



NATURE 



[February 23, 1922 



.urchins, for they are not sessile animals, but move 

 actively, their vertical range of migration during the 

 course of an hour being far in excess of this figure. 



The possibility of tidal influence could be tested by 

 keeping urchins in a floating cage. If the lunar 

 reproductive cycle were thereby abolished, the tidal 

 connection would be demonstrated ; a contrary result 

 from the experiment, however, would not dispose of 

 a possible influence of the tides, for an established 

 rhythm in a physiological process is often persistent 

 after the original cause has been removed. Unfortu- 

 nately the experiment was impracticable with Diadema 

 owing to its size. Full-grown specimens measure 

 more than one foot from tip to tip of the spines, 

 and it was impossible to obtain large enough floating 

 boxes to contain a hundred or more individuals. 1 

 intend, however, to seek further evidence regarding 

 the possible eff^ect of tides by studying Echinoids in 

 localities with greater and smaller tidal ranges than at 

 Suez. I am convinced, though, that if a similar lunar 

 reproductive cycle exists in the sea-urchins at Naples 

 or at Plymouth it is very little pronounced; for I 

 have made use of the Echinoids at these places to 

 obtain spermatozoa and ova for other experimental 

 purposes for months on end without ever noticing a 

 rhythmic variation in the condition or quantity of the 

 genital products. At Suez the period in each lunar 

 month when spermatozoa and eggs are unobtainable 

 would necessarily force itself upon the notice of the 

 investigator. 



The possibility of a direct effect of the light of the 

 moon on the Echinoids could be tested bv keeping 

 specimens in the dark. Although the large size of 

 Diadema again precluded this experiment at Suez, I 

 intend to carry it out in another place with a smaller 

 Echinoid. If the light has an effect it must necessarily 

 be more constant in the cloudless summer nights of 

 Egypt than in Europe. It was thought possible that 

 the light of the moon might act by causing the urchins 

 to feed either more or less than usual on moonlit 

 nights. A systematic examination of gut contents 

 showed that this was not the case. 



Other marine animals popularly believed in Egypt 

 to vary with the moon are mussels and crabs. Con- 

 trary to the case of the sea-urchins, I have found these 

 beliefs to be without foundation. 



Now it is obvious that the periodic spawning of 

 Diadema must be reflected in the plankton of the Gulf 

 of Suez. The plutei must vary in quantity and in 

 stage of development with the phases of the moon. 

 By an examination of plankton from different parts 

 of the world I hope to discover which of the animals- 

 having pelagic larvae show a lunar reproductive cycle. 



The best known example of lunar reproductive 

 periodicity at the present time is the Palolo worm. 

 In the South Pacific these Polychaetes swarm at the 

 surface of the sea to discharge their genital products 

 at the third quarter of the October and November 

 moon fFriedlandor. Biol. CentralhL, iSqS-Tgoi). In 

 Japan another Palolo swarms at both full and new 

 moon, i.e. at the spring tides (Izuka, Journ. Coll. 

 Sci. Tokyo, 1903), while in the Atlantic a third snecies 

 'has similar habits (Mayer, Carnegie Inst. Pubs., 

 looq). Odontosyllis in Bermuda (Gallowav and Welch, 

 Tr. Am. Micr. Soc, iqti) and British Columbia 

 (Potts, Proc. Camb. Phil. Soc, 1913), and Nereis 

 (Lillie and Just, Biol. Bull., 1013) and Platvnereis 

 (Just, Biol. Bull., iqi4) at Woods Hole, Massa- 

 chusetts, have been shown to swarm at one definite 

 phase of the moon, whereas Nereis at Naples (Hempel- 

 mann, Zoologica, 1911) swarms at about the first 

 and third quarters. The latter bi-lunar, i.e. 

 iapparentlv tidal, periodicity is remarkable, since the 

 tidal range at Naples is much smaller than at Woods 

 NO. 2730, VOL. 109] 



Hole. Another Polychaete, Amphitrite, lays its eggs 

 at new and full moon spring tides at Woods Hole 

 (Scott, Biol. Bull., 1909), as does also the Turbellarian 

 Convoluta in Brittany (Gamble and Keeble, Quart. 

 Journ. Micr. Soc, 1903). 



To my knowledge the only other case of reproduc- 

 tive periodicity in animals correlated with the lunar 

 period is in the human race. Arrhenius (Skand. Arch, 

 f. Physiol., 1898) showed statistically that there exists 

 a low correlation between the menstrual period and 

 the (tropical) lunar month. In addition, he found 

 traces of a consequent tropical lunar periodicity in 

 birth frequency. 



The only authentic cases of lunar rhythm in the 

 reproduction of plants seem to be among the algae. 

 In North Carolina Dictyota produces one crop of 

 sexual products in each lunar month (Hoyt, Bot. Gaz., 

 1907). The same plant at Naples (Lewis, Bot. Gaz., 

 1910), and at Plymouth and Bangor (Williams, Ann. 

 Bot., 1905), has a tidal reproductive rhythm, i.e. two 

 cycles per lunation, as is also the case with Sargas- 

 sum (Tahara, Bot. Mag., Tokyo, 1909). 



Popular beliefs in the influence of the moon on 

 plant growth are world-wide, although most of them 

 are probably on a par with the superstition that 

 a waxing moon increases and a waning ^ moon 

 decreases any process, such as "the acquisition of 

 wealth, the growth of corns, nails, hair, etc In 

 Egypt it is said that melons and other fruits of the 

 Cucurbitaceae grow most rapidly on moonlit nights. 

 The belief that sowing and planting must be done in 

 a waxing, and reaping and cutting in a waning,^ moon 

 is very widespread. As regards cutting, experiments 

 made recently in Trinidad by Rorer have proved the 

 superstition to be without foundation. It is conceiv- 

 able, nevertheless, that moonlight may have a photo- 

 synthetic effect. Kofoid (Bull. 111. State Lab. of Nat. 

 Hist., 1903 and 1908) and Allen (Univ. Cal. Pubs. 

 Zool., 1920) have found a maximum frequency of 

 plankton algae in certain North American rivers oc- 

 curring at full moon. Kofoid attributes this to lunar 

 photosvnthesis, quoting experiments of Knaute (Biol. 

 Ceritralbl., 1898) in support of his hypothesis. Oxving 

 to the great importance of this possibility, and since 

 Knaute obtained a surprisingly large "amount of_ photo- 

 synthesis in moonlight, I am at present repeating his 

 work. 



I should be grateful if readers of Nature would 

 communicate to mp popular beliefs in lunar in- 

 fluence on animals or plants. It is possible that some 

 of them mav prove upon investigation to be as well 

 founded on fact as the case of Diadema. 



H. MuNRO Fox. 



School of Medicine, Cairo, January 25. 



Research Degrees and the University of London. 



There are at present four degrees in the faculty 

 of science of the University of London which may 

 be granted for a research thesis, namely, D.Sc, 

 Ph.D., M.Sc, and (in exceptional cases only) B.Sc 

 If a recent report by a sub-committee of the Academic 

 Council should be finally adopted by the University, 

 these four will be reduced to two, D.Sc. and Ph.D., 

 while a new series of examinations will be introduced 

 for M.Sc. As I feel very strongly (with many of my 

 geological colleagues) that this would be a mistaken 

 nolicy, I venture to ask for space in the columns of 

 Nature to state my reasons for that feeling. 



It would scarcely be necessary to refer to the case 

 of B.Sc. by research but for the serious misconcep- 

 tions on the subject shown in the sub-committee's 

 report. The granting of this degree is a very rare 

 event, and I have no personal knowledge of any case 



