August 12, 1922] 



NA TURE 



2I 5 



Pairing and Parthenogenesis in Saw-flies. 



As the result of recent experimental studies in the 

 biology of saw-flies of the family Tenthredinidae, with 

 particular reference to their parthenogenesis, I have 

 been struck by the dearth of information as to their 

 mating habits. My observations have revealed a 

 novel point which I wish to record ; and, in order to 

 discuss its significance, I present first a brief summary 

 of certain points relative to saw-fly breeding. 



1. Females of Athalia lineolata Lep., on collecting, 

 were found to be greatly outnumbered by the males; 

 they paired frequently and probably were polyan- 

 drous. (The writer has a paper on this in the press.) 



2. In certain species, e.g. Pristiphora pallipes Lep., 

 the male is excessively rare. 



3. In certain species, e.g. Allantus (Empkytus) 

 pallipes Spin., no male has been taken or bred. 



4. Some 30 species produce males only by partheno- 

 genesis ; some 13, females only by parthenogenesis ; 

 about 6 produce both sexes similarly. (See lists of 

 Cameron and Enslin.) 



5. A large number of species other than the above 

 are facultatively parthenogenetic, and future work 

 will greatly extend the list. (See work of Miss 

 Chawner and the writer.) 



6. Certain species, in captivity at any rate, refuse 

 to pair. (See work of Fletcher, Miss Chawner, and 

 the writer.) 



7. Females of Platycampus laridiventris Fall., after 

 persistently ignoring the males, may lay eggs 

 parthenogenetically while kept with their food plant 

 under a glass vessel and in the presence of the males. 

 (Writer's observation.) 



S. Virgin females of Phymatocera aterrima Kl., 

 after laying eggs (which gave healthy larva?) paired 

 with males presented to them. Unfortunately the 

 females were about spent before pairing and did not 

 lay again. 



9. A virgin female of Nematinus luteus Panz., after 

 laying eggs which gave healthy larvae, paired with a 

 male and then, subsequently, laid other eggs. Un- 

 fortunately, through the wilting of the alder twigs, 

 which I was compelled to use instead of young trees, 

 I have been unable to rear the presumably fertilised 

 eggs which were laid after the asexual batch. I 

 cannot state, therefore, whether this female's par- 

 thenogenetic offspring are different in regard to sex 

 ratio or in germinal constitution from the offspring 

 of the batch produced after fertilisation. This I am 

 hoping to elucidate later in this season by the use of 

 other species. 



Points 1-4 are fairly well known, but Nos. 5 and 6 

 are probably known only to the few workers who have 

 studied the group, while Nos. 7, 8, and 9 result from 

 my studies, and being new, so far as I am aware, 

 they form the raison d'etre of this note. 



These facts warrant the suggestion that in saw-flies 

 the total sexual or partial sexual indifference of the 

 sexes is a method for regulating (a) the numerical 

 balance of the sexes and, ipso facto, (b) the amount of 

 amphimixis necessary for the preservation of the 

 species. 



Again, the female saw-fly, by refusing or accepting 

 fertilisation, or by first refusing the male, then laying 

 asexually, next accepting fertilisation and, lastly, 

 laying presumably fertilised eggs, achieves the same 

 ends as the queen bee, which after fertilisation, pro- 

 duces females and workers from fertilised eggs, and 

 males (drones) from unfertilised eggs. (This assump- 

 tion, of course, rests upon the fact that the chromo- 

 some complement of the females and workers is twice 

 that of the drones.) 



The survival value of the parthenogenetic pro- 

 duction of females and of both sexes in certain 



NO. 2754, VOL. I 10] 



species is not difficult to apprehend, but the pro- 

 duction of males only has presented a seemingly freak- 

 ish and puzzling problem. The solution has been 

 obscured by its being a laboratory observation, 

 isolated, and uncorrelated with a knowledge of what 

 occurs in nature or with such a fact as I have just 

 presented. Doubtless males only may be produced 

 in nature by certain females, but my observation 

 suggests two further possibilities — that (1), in nature, 

 certain females of a species may lay male-producing 

 eggs and, subsequently, after fertilisation, eggs 

 producing both sexes ; (2) a certain number of females 

 are set apart as virgins for producing males only, 

 while others pair and produce both sexes. (There 

 is too, of course, the remote possibility that fertilised 

 eggs may yield only females sometimes.) 



With such a range of possibilities for the production 

 of the sexes the process of gametogenesis in saw-flies 

 is likely to prove more complicated than has 

 hitherto been supposed and may account for recent 

 anomalous results. 



Assistance in prosecuting the work has been 

 rendered through a grant from the British Association. 

 A. D. Peacock. 

 Zoological Dept., Armstrong College 



(University of Durham), Newcastle-on-Tyne. 



Some Significant Relations in the Quantum 

 Theory of Spectra. 



The non-radiating orbits of Bohr's atom are given 

 by the relation 



a n = 5 ^ (i) 



The frequency of the wave emitted in jumping from 

 one orbit to another is given by the energy relation 



/^'„.„,_^„ = A„ +m -A„, . . . (2) 



2Tr 2 uie 2 K 2 

 h» 



Gr£>- 



(3) 



The convergence frequencies, given by the values 

 of m equal to infinity in (3), are given by 



27r 2 we 2 E 2 , . 



"«= jfr.V (4) 



and correspond to radiation emitted by an electron 

 falling into the orbit a„ from rest at infinite distance. 

 The frequency v„ involves t„ for only one orbit, 

 and may be regarded as associated with that orbit. 

 Between (1) and (4) we have immediately 



fly* = —7 = constant. . . (5) 



Or, the frequency associated with an orbit is inversely 

 proportional to the radius of the orbit for the same 

 kind of atom. 



The average kinetic energy of a particle describing 

 a S.H.M. of amplitude a„ and frequency »„ (instead 

 of the orbital frequency « = 47r 2 wg 2 E 2 /r>//. 3 ) is 



mir 2 a,, i v n 2 = =-5 — = constant . . (6) 



«- 



for the convergence frequencies of the same atom. 



In his theory of chemical reaction and reactivity 

 (Transactions of the Faraday Society, vol. xvii. 

 Part 3, May 1922) Baly assumes (1) that an atom can 

 gain or loseenergy in terms of the elementary quantum 

 of energy ; (2) that the physical change, attending 

 such gain or loss of energy, occupies a definite period 

 of time which is the same for all atoms ; (3) that the 

 elementary quanta of all atoms are integral multiples 

 of a fundamental unit which very probably is the 

 elementary quantum of the hydrogen atom. 



