342 SECTIONAL TRANSACTIONS.— D. 



Dr. B. P. UvAROV. — Cyclic Polymorphism in Locusts, and the Periodicity 



of Locust Invasions. 



While the technical methods of controlling locusts are well developed and very 

 effective, a successful organisation of anti-locust campaigns meets with many 

 difficulties. The main difficulty lies in the fact that locusts are not a permanent pest, 

 but may be absent from a country one year, and appear in enormous swarms in the 

 next. For instance, the Desert locust, a species alluded to in the Bible, invaded the 

 whole of North and ilast Africa, Persia, India, Iraq, Palestine and Turkey in 1914-1916, 

 and then nothing was heard about it for over ten years. Since 1926-1927 a new 

 outbreak started, and, by 1929-1930 Africa, from Tanganyika to the Mediterranean, 

 and S.W. Asia as far north as Transcaucasia and Turkestan, were overrun by 

 devastating swarms. 



Such sudden outbreaks involving whole countries find some of them not fully 

 prepared to meet the danger, and during the recent invasion truly gigantic efforts 

 were required to save the crops. An effective organisation of an anti-locust campaign 

 cannot be improvised at a moment's notice, while it is clearly impossible to keep the 

 organisation in readiness during long intervals between invasions. 



The key to the solution of the locust problem is, therefore, in finding out the laws 

 governing periodic outbreaks of locusts. Recent work in this direction in Russia, 

 South Africa, Sudan and elsewhere, proved that the periodicity of locust outbreaks 

 is intimately connected with the fact that all known species of locusts occur in two 

 forms, or phases. These forms differ from each other in a number of structural and 

 colour characters, but more particularly in the habits. During the intervals between 

 outbreaks locusts are represented by the solitary phase, which is a harmless grass- 

 hopper without definite social habits. When the outbreak begins, the solitary phase 

 is transformed into the gregarious one ; the individuals of this phase form dense 

 swarms and undertake long migrations. Experimental work on phases has shown 

 that the solitary phase can be turned into the gregarious one, if the locusts are kept in 

 a crowded condition ; reversedly, one can obtain the solitary phase by breeding 

 gregarious individuals under isolated conditions. 



Periodic outbreaks of locusts, thus, depend on the cyclic transformation of these 

 insects from one phase into another, and back again. The actual factors causing 

 and favouring the transformation are still insufficiently known, but it is clear that 

 the problem of the successful control of locusts cannot be solved until these factors 

 are thoroughly investigated. 



A special Locust Committee has been appointed recently by the Government to 

 consider the locust problem, and it was decided to organise exhaustive investigations 

 into the question of periodic outbreaks and their causes. It is hoped that the actual 

 work will begin shortly, and this concentrated scientific attack on locusts should 

 produce results of great practical value in the shape of some means of foreseeing and 

 preventing locust invasions, which would mean an enormous saving in crops, human 

 energy and money for a large number of countries affected by the plague. 



Dr. Nellie B. Bales.- — The Mandible of Foetal Elephants. 



A study of three foetal specimens of the Elephant, of which two are African and one 

 Indian, reveals changes in the development of the mandible of a very definite character. 

 Modifications in the growth of the simple generalised foetal jaw are partly due to the 

 gradual assumption of the highly specialised features of the Proboscidean mandible, 

 and this is to be expected. But the three foetal specimens exhibit also a condition 

 unique amongst modern mammals, in that the jaw bends ventralwards anterior to the 

 first deciduous premolar (DP 2), thus turning away from the upper jaw. Now this 

 is the type of jaw which, according to Palaeontologists, occurred in the Elephant's 

 ancestors, those long-jawed beasts like Tetrabelodon. The foetal Elephant, therefore, 

 retains this peculiar ancestral character and affords a clear confirmation of the work 

 of Palaeontologists on the lineage of the Proboscidea. 



A comparison between the mandibles of the three foetuses and of young and old 

 post-natal stages shows that the down-turned pre-alveolar region of the jaw enlarges 

 up to about the middle of the gestation period, since the oldest foetus is about this age 

 and has the longest type of jaw. Between this stage and the full-term foetus (about 

 22 months) we have neither specimens nor records, so that we do not know how the 

 metamorphosis occurs. The shortening of the pre-alveolar region and the downward 



