A REVISION OF THE GENUS LOCUSTA, L. 153 



migratoria sent from Southern Celebes by Dr. Roepke to the Imperial Bureau of 

 Entomology, which had the following note attached : "A Locusticl from S. Celebes 

 (Pangka djene) appearing there in small swarms and causing damage to the natives' 

 plantations, such as rice, corn, etc." 



The Theory of Phases. 



Though the above recorded facts by no means exhaust the points to be considered 

 in connection with the problem of the interrelations of migratoria, danica and 

 migratorioides, they yet permit us to make an attempt to find out the best explanation 

 at present possible. The following theory seems to me to agree in a rather satis- 

 factory manner with all the facts known at present, though some modifications of 

 it may prove to be unavoidable when new data are available. 



As a starting point, I take it as positively proved that the three forms 

 cannot be separated specifically and that they represent taxonomic units of lower 

 grade than the species, which must be called, according to the law of priority, 

 L. migratoria, L. They are, however, quite distinct from each other, though 

 connected by transitional forms. 



What term, then, should be applied to them ? They are certainly not mere 

 individual aberrations — as they are often assumed to be by other authors — since 

 they are rather constant in their average morphological characters and still more 

 so in their biology ; nor can we call them subspecies, i.e., geographical races, as 

 they are found together in the same locality ; nor are they seasonal forms, since 

 the transformation of one of them into the other has evidently nothing to do with 

 season. The only more or less suitable term for them is " morpha," in the sense 

 proposed by A. P. Semenov-Tjan-Shansky,* who proposed to apply this name to 

 such forms of a species that present a direct result of the immediate external 

 influences on the individual insect during its development, and which therefore do 

 not appear in succeeding generations if the original influence ceases. Under this 

 definition come seasonal forms, which may be obtained by the artificial application 

 to developing individuals of certain factors causing their appearance under natural 

 conditions ; the forms resulting from feeding larvae by some special food, etc. The 

 same term may be applied, according to the personal opinion of A. P. Semenov- 

 Tian-Shansky, expressed in his letters to me, to the case of the Locusta forms. It 

 seems to me, however, that the term " morpha " is rather vague, and moreover 

 we are yet far from knowing whether the transformation of one form into the other 

 is due to some immediate external influence or to some yet unknown internal cause ; 

 I think, therefore, that the term " phase " (La.tm phasa ; abbreviation — ph.) suggested 

 to me by Dr. G. A. K. Marshall is more appropriate, and its meaning will be made 

 clear in the course of the explanation of my theory. 



There is no doubt in my mind that migratorioides is the oldest form of the species, 

 since its morphological and colour characters are far more constant in comparison 

 with the more plastic migratoria, to say nothing of the extremely variable danica. 

 The permanent breeding regions of migratorioides have never yet been investigated ; 

 the only description of breeding places of this form in the Malay States given by 

 H. C. Pratt [I.e., pp. 6-7) must obviously be referred not to the permanent breeding 

 grounds, but merely to the places where the oviposition of emigrated swarms took 

 place. All we know at present concerning the permanent breeding areas of 

 migratorioides is based on the records of the occurrence of its swarms ; and these 

 data enable us to state that the best conditions for the development of this form 

 seem to be present in tropical countries with a rather damp and hot climate, but 

 undoubtedly not in forests. Since, on the other hand, these breeding grounds seem 

 to be yet undiscovered, we may presume that they are also not in open, grassy land, 



* Die taxonomischeii Grenzen der Art und ihrer Unterabteilungen. Berlin, 1910. 

 (3442) M 



