;oN 



NATURE 



[December 19. 1918 



usual low-speed engine. Mr. Ricardo suggests 

 that piston design in particular Is looked on from 

 such different angles by the two schools as to lead 

 to \<i\ marked differences in engine types. A 

 heavy piston means high inertia forces at the 

 beginning and end of each stroke; this means a 

 stout connecting-rod; both these in turn call for 

 a strong and heavv crank requiring massive bear- 

 ings, and al once we are led to the ordinary gas- 

 engine of pre-war davs. The aero-engiiie has 

 developed a piston suitable lor beavj loads and 

 high speeds. It is surely unlikely that designers 

 ol other types of internal-combustion engine will 

 lail to draw thi' obvious conclusion. 



The war may be expected to leave its mark on 

 internal-combustion engine design in two ways: 

 first, by greatly lightening the motor-car engine, 

 s.> thai its weight per horse-power may not corn- 

 pan- so unfavourably with that of aero-engines; 

 and secondly, by making the slow-speed stationary, 

 or nearly stationary, gas- or oil-engine a much 

 less cumbrous machine. 



Evolution in engine practice has long been 

 towards ever-increasing speeds. The old beam- 

 enginesof the early part of last century gave place 

 to an engine of much higher speed with hundreds, 

 instead of tens, of revolutions per minute. The 

 higher speed meant, for equal horse-power, less 

 total force on the piston, hence a less diameter of 

 piston, a smaller and lighter engine. Now again 

 we find this same evolutionary process. at work- 

 piston speeds are rising and the weight per horse- 

 power ratio grows less. 



In view of the specially intense interest which 

 the agricultural industry will have for humanity 

 during the next term of years, it is important to 

 consider how far our recent increase in knowledge 

 ol the potentialities of the internal-combustion 

 engine may be harnessed to this work. Ford in 

 America has done much — but mainly on what may 

 be termed pre-war data. Much remains to be 

 done in this coming post-war period. High piston 

 speeds, light reciprocating parts, and tin- use of 

 high-grade steels should, combined, produce 

 ultural machine as efficient lor its purpose 

 as the motor-car and aeroplane have become. The 

 annual output of high-speed internal-combustion 

 engines in this country is at present at the rate of 

 some 10,000,000 h.p. annually. A large part of 

 this has been for air work; a smaller fraction will 

 suffice now. Here is to be found a lm-c.u oppor- 

 tunity for the internal-combustion engine in fresh 

 enterprise in new fields. H. E. \V. 



Nl RSING HABITS OF ANTS IND 

 TERMITES. 

 A RECENT paper by Mr. W. M. Wheeler, in 

 ^~* the Proceedings of the American Philo- 

 sophical Society, Philadelphia, gives some interest- 

 ing details of the behaviour of certain ants in the 

 care of their offspring. The larvae of the primi- 

 tive subfamily PonerLnae an- fed, not, as in the 

 ease of the most highly specialised ants, with 



Food regurgitated bv the workers, but with frag- 

 ments of insects. Speaking ni a species of this 

 NO. 2564, VOL. I02"| 



subfamily common in central Texas, Mr, Wheeler 

 says : — 



These larvae are placed l>v the ants on their broad 

 hacks, and their heads and necks are folded over on 

 to the concave ventral surface, which serves as a taM< 



or trough on which the food is placed bv the workers. 



In the case of another species, as soon as the 

 food is in place il is sometimes covered by the 

 larva with a copious discharge of a secretion con- 

 taining a proteolytic ferment, by means of which 

 the food undergoes extra-intestinal digestion. 

 Mr. Wheeler adds the curious observation that 

 this liquid is eagerly lapped up bv the nurses. 



The larvae of four species of ants belonging to 

 the subfamily Myrmecinte were collected bv Mr. 

 Lang in the Belgian Congo. In three of these, 

 remarkable exudatory appendages exist, some of 

 which consist of a basal enlargement tilled with 

 fat-cells, and a slender, tubular distal portion 

 containing a granular liquid which the author 

 thinks can only be interpreted as an exudate 

 derived from the fat-cells, and capable of being 

 filtered through the cuticula of the appendages 

 by means of the pressure exerted by an elaborate 

 system of muscles. That the chitinous envelope 

 of these structures is not necessarily impervious 

 to the passage of a secretion is shown bv the 

 researches of Holmgren, Biedermann, Kapsov, 

 Casper, and others. From the ontogenetic and 

 phylogenetic history of these appendages, and 

 especially from the fact that the} appear to lie 

 developed in inverse ratio to the salivary glands 

 used in extra-intestinal digestion, Mr. Wheeler 

 concludes that their secretion, like that of the 

 salivary glands in the Ponerina\ is capable of 

 furnishing nutriment to the nurses, the benefit of 

 the feeding habit being therefore reciprocal. This 

 conclusion he considers to be supported bv the 

 observations of YVasmann on the Staphylinid 

 beetle Kertogaster inflata, which inhabits the nests 

 ol termites. In this larva the fat-body produces 

 an 1 nidation which, after passing through a layer 

 of hypodermis, reaches the surface tin, ugh the 

 cuticle. Similar phenomena are present in other 

 beetles and Hymenoptera which frequent the nests 

 ol ants or termites, as recorded by Traglrdh ; 

 while Holmgren has found that, quite apart from 

 their guests, termites feed to a large extent on 

 the exudation furnished in different degrees bv 

 the several castes of their own species. 



For this reciprocal feeding, whether within or 

 without the limits of tin. same species, Mr. Wheeler 

 proposes the term " trophallaxis. " The practice 

 has, he considers, an important bearing on the 

 substitution of the social for the solitary habit 

 in various species of Hymenoptera. The various 

 trophallactic relations existing in communities of 

 ants arc grouped by him as follows: (i) Trophal- 

 laxis between mother or adult worker and larval 

 brood; (_:) between adult ants (mutual regurgita- 

 tion); (3) 1 iet w ecu ants and true guests ; (4) between 

 ants ol different specie's. Besides these reciprocal 

 relations there is the ordinary trophic connection 

 between ants and other insects outside the nest 

 (as aphides and certain LepidopterOUS larva'), and 



