16 BULLETIN 143, UNITED STATES NATIONAL MUSEUM 



worker larvae. Brehm° reared a specimen of the dipteron Anthrax semiata 

 or morio L. from the cocoon of a bumblebee. He thought the variations in the 

 size of this species vpere due to different quantities of food which were available 

 to the larvae. Stepanow" found that the larvae of the bombyliid Systoechus 

 leucophaens Meigen had different sizes which he thought depended upon the 

 quantitj' of food in the egg masses of the orthopteron, Stauronotus vastor 

 Stevens, upon which the larvae feed. The adult flies also exhibited the same 

 variation. Standfuss ' reared the larvae of Aglia tau L., a saturnid moth, on a 

 subnormal amount of food and obtained adult moths which were much reduced 

 in size. Bordage ^ reports a similar experiment with Atella pholonta, a vanessid. 

 Rudow" observed the variations in size which are present in the species of 

 various genera of the aculeate Hymenoptera and states that the quantity of 

 food available to the larvae of these forms is undoubtedly the cause of the 

 variations in size. Herms ^° conducted some feeding experiments with a sar- 

 cophagid fly, Lucilia caesar L., in which he allowed the larvae to consume as 

 much as they would, and varied the length of the time of feeding. These time 

 periods varied from 36 hours, which seemed to be the lower limit at which 

 adults could be secured, to an optimum period of from 60 to 72 hours. He 

 obtained adult flies varying from a minimum size with 36 hours' feeding to the 

 normal size which were fed for a period of 60 to 72 hours. Wodsedelak" has 

 carried on some interesting experiments with the larvae of a dermestid, 

 Trogoderma tarsale, in which he has been able to vary their size from large to 

 small by starving, and from small to large by feeding again. Nc data are 

 available as to the effect of this sort of feeding on the adult beetles. 



In all of the cases which have been reviewed it is obvious that the varia- 

 tions have to do with a single species. If a graph is made representing the 

 frequency and range of any of these variations the resulting curve is unimodal, 

 that is, all of the specimens exhibiting variation group themselves progres- 

 sively around the niost abundantly represented form. If, however, the cir- 

 cumstances should be such that when a graph of the frequency and range 

 of the variation is made, the resulting curve is bimodal, it is not so apparent 

 that one is dealing with a single species. In fact, from an examination of 

 museum specimens only, one might be led to the conclusion that two species 

 were represented rather than one, and an investigation of the organism and 

 its enviroment would be necessary before one could arrive at the true state 

 of affairs. In cases of this kind the variation may appear to be discontinuous 

 but a study of the data seems to show that it is more correct to consider it 

 as a continuous variation of the bimodal type, and such variation may well 

 be designated as bimodal. It is conceivable that variations of this kind occur 



° Brehm, Alfred Edmund. 1869. Illustrirtes Thierlebeii, I. Auflage 6. Wirbellose 

 Thiere. Ilildburghausen. 



^ Stepauow, P. G. 1882. Ueber Metamorphosen bel Dipteren der Familie Bombylldae, 

 Arbeit, dor Naturforscber-Gesellsch. bei der IJnivers. zu Cbarkow, vol. 15 (1881), pp. 1-9. 



'' Standfuss, M. 1896. Handbucb der paliiarktiscben Grossscbmetterlinge liir Forscbcr 

 und Sammler. 2 ed. (392 pp.). Jena 



* Bordage, Edmond. 1899. Experiences sur la relation qui existe entre la couleur du 

 Mileu et la couleur des Chrysalides de certains Wpidoptferes, Proc. Fouith Int. Cong. Zool. 

 Cambridge, pp. 235-244. London. 



" Rudow. 1900. Weiterer Beitrag zu den Grossenverhaltnissen der Insekten, Insekt.- 

 Bcirse, vol., 17, no. 24, pp. 188-189. 



1900. Ueber die Grossen-Variation bei Insekten, Insekt.-Borse, vol. 17, No. 2, pp. 10-11. 



"> Herms, William B. 1907. An Ecological and Experimental Study of Sarcophagidae 

 with Relation to Lake Debris, Journ. Exp. Zool., vol. 4, pp. 45-83. 



" Wodsedalek, J. E. 1917. Five Years of Starvation of Larvae, Science, vol. 46, pp. 

 366-367. 



