July 15, 1922] 



NA TURE 



95 



in use at a number of observatories. He claims that 

 the results show, first, that the Carnegie Institution 

 standards are in every way satisfactory, and second, 

 that " the absolute precision obtainable with carefully 

 designed magnetometers and (dip) inductors, pro- 

 vided instruments are carefully used and comparisons 

 are made with reliable standards at least every two 

 or three years, is of the order o'-2 in declination and 

 inclination and of the order 0-00015?! (i.e. 37 in 

 England) in horizontal intensity." If 'this be true, 

 the gain in accuracy to be hoped for from coil instru- 

 ments is not great. If, however, as stated on p. 468, 

 a complete observation of H with the coil instrument 

 occupies only 2 minutes, its use at an observatory 

 would represent a great economy of time, always 



provided little time is spent on keeping the apparatus 

 up to the mark. 



However this may be, what is really more wanted 

 is a coil instrument for measuring V (vertical force). 

 Base line values of V curves are at present dependent 

 on dip circles or inductors. Even if the accuracy 

 claimed by .Mr. Fleming for dip inductors be con- 

 ceded, it must be remembered that an error of o'-2 

 in the dip at a place where the value of H is only 0-03 

 (the approximate value at the base station of the 

 Australasian Antarctic Expedition 1912-13) leads to 

 an error of about 907 in V. Thus a coil instrument 

 which could give V directly, to within ±57 even, would 

 be an immense improvement on a dip inductor for 

 use in high latitudes. 



New Social Coleoptera. 1 



By Dr. A. D. Imms. 



T F we regard as truly social only these insects in 

 * which the parent, or parents, live with their 

 offspring, protecting and feeding them, there have 

 been known hitherto but three groups of beetles 

 which come into this category, namely, the Platy- 

 podida?, Scolytida-, and Passalida?. Prcf. W. M. 

 Wheeler has recently added to the list two genera of 

 Silvanid beetles belonging to the family Cucujida, 

 discovered by him in British Guiana. The beetles 

 in question are Coccidotro pints socialis and Euiiau- 

 sibiits wheeler i both of Schwartz and Barber. The 

 bulk of his observations concern the first-mentioned 

 insect, the other species being apparently rare. 

 The beetles enter the hollow petioles of a Leguminous 

 tree Tachigalia and either bore their way in, or gain 

 admittance through perforations previously made by 

 other insects. They enter either as a single pair, 

 or one beetle enters and is very soon joined by an 

 individual of the opposite sex. Upon taking posses- 

 sion of their future habitation the beetles remove .un- 

 loose pith, or the remains of previous tenants, by 

 pushing this debris into the pointed ends of the cavity 

 by means of their flattened heads. This behaviour 

 brings the insects into contact with the outermost 

 layer of pith adhering to the walls of the cavity, 

 and certain strips of nutritive parenchyma. The 

 latter tissue forms the food of the beetles, and is 

 also shared by young Coccida? of the species Pseudo- 

 coccus broiiieliir, which soon begin to enter the petiole- 

 cavity. By means of the feeding action of the beetles, 

 the strips become converted into grooves, the coccids 

 stationing themselves in a row in each groove. The 

 beetles carefully avoid soiling their food material and 

 store their frass in the areas between the grooves. 

 They lay their eggs along the frass ridges, and the 

 larvae which hatch out feed upon the same nutritive 

 parenchyma as their parents. When mature, they 



1 W. M. Wheeler, " A Study of some Social Beetles in British Guiana 

 and of theil Relations to the Ant-Plant Tachigalia." ZoolOgica, New York, 

 vol. iii. Xos. 3-11, Dec. 24, 1921. 



construct brown cocoons within which pupation 

 occurs. The beetles emerging from the latter remain 

 in the petiole with the original pair ; they mate ami 

 produce eggs and larva? in turn, thus leading to the 

 climax stage of the colony, which may eventually 

 consist of several dozens of beetles of both sex.-,, and 

 many larva? and pupa- in all stages of development. 

 The Coccida? also increase in number, so that the 

 cavity of the petiole sometimes becomes crowded 

 with inmates. In the meantime, the old and 

 exhausted beetles die off, and their bodies are con- 

 signed to the refuse accumulations ahead}- mentioned. 

 When this crowded condition is reached, beetles 

 begin to leave the colony either singly or in pairs and, 

 seeking other petioles, thus found new colonies. 



Both the larva? and imagines of the Coccidotrophus 

 solicit honey dew from the coccids by " stroking " 

 the latter by means of the antenna?. The relations 

 of the beetle to the coccids, moreover, are physiologi- 

 cally similar to those of symphile beetles to host 

 ants that supply them with regurgitated liquids. 

 Coccidotrophus, like the symphiles, has specially 

 modified antenna? and labium, such modifications 

 occurring in both the larva' and adults. This type 

 of relationship with Coccida? has not been noted 

 hitherto in any Coleoptera and, apart from ants, very 

 few insects are known to have developed the ability 

 to solicit honey dew from among the Homoptera. 



It appears that the Sylvanids have a more primitive 

 social life than any of the three families of beetles 

 previously alluded to, but there is no definite 

 preparation of larval food by the parents. Their 

 colonies represent a stage in social development 

 intermediate between the families mentioned and 

 the merely gregarious species of Cucujida?. For 

 further details, and many interesting observations 

 on the numerous and heterogeneous " bioccenose " 

 of other insects associated with the plant Tachigalia, 

 the reader is referred to Prof. Wheeler's original 

 paper. 



Spectroscopic Studies of Stellar Velocities. 1 



By Dr. William 



T N order to determine the distribution and motion 

 -*■ of stars in space it is necessary to know four 

 important facts about each star. The first is its 

 position, known as its Right Ascension and Declina- 

 tion ; the second is its proper motion, i.e. the move- 



1 "The Radial Velocities of 594 Stars," Publications of the Dominion 

 Astrophysical Observatory. Victoria, B.C. (vol. 2, No. 1), bv J. S Plaskett 

 W. E. Harper, R. K. Young. H. H. Plaskett (Ottawa. 1921)". 



NO. 2750, VOL. I IO] 



J. S. LOCKYER. 



ment at right angles to the line of sight ; the third is 

 the radial velocity or movement towards or away from 

 the earth ; and lastly, the parallax or distance of the 

 star from the earth. 



During the last few years the accumulation of a 

 large amount of such data, extending over many 

 years, has led astronomers to the important problem 

 of investigating the systematic motions of the stars 



