ORIGIN OF CASTES OF TERMITES 91 



colonies of all ages, with or without royal pairs, on various kinds and 

 amounts of food — proctodeal food dissected from workers or in other 

 cases from royal forms, stomodeal food from the same sources, saw- 

 dust to which various nutritious ingredients had been added — but in 

 spite of all I cannot feel perfectly sure that I have influenced in any 

 unusual way the growth of a single individual. 



It is interesting to note that these careful experiments produce 

 only negative evidence for the food hypothesis. 



Desneux has written a number of papers on the biology and 

 the classification of termites. In the Genera Insectorum, 

 Isoptera ('04), he states his view that the different castes arise 

 from eggs that are identical, that the newly hatched 'larvae' 

 are all alike, and that the probable cause of the differentiation 

 of the young 'larvae' is a particular diet. 



Escherich ('09) reaffirms Grassi's view of the origin of termite 

 castes : 



Gehen wir auf das erste, jiingste Stadium zuriick, so gibt es iiber- 

 haupt noch keine Unterschiede, sonclern sind sich alle Jugendformen 

 vollkommen gleich. Nicht nur ausserhch, sondern audi ihren Werte, 

 ihren Entwicklungspotenzen nach, d. h. die eben ausgeschliipften Larven 

 sind noch vollig indifferent und konnen sich sowohl zu Arbeitern, als 

 Soldaten, als audi geflligelten entwickeln. 



Escherich believes that food plays the chief role in the differ- 

 entiation of the castes, but he assumes, with Weismann, that 

 food is not the direct cause, but merely the stimulus which brings 

 into being the potentialities of one or another of the different 

 castes, these potentialities being present in every egg. 



Holmgren ('09), who has written exhaustively upon the syste- 

 matic position and the anatomy of termites, explains the origin 

 of castes by his exudation theory (Exudat-theorie). According 

 to this view the newly hatched nymphs are 'indifferent' or all 

 alike in appearance, but from the beginning some nymphs may 

 receive a little more food and may produce a little more exudation 

 than the others, and are consequently more frequently hcked 

 and better cared for by the workers, and finally develop into 

 the 'small headed' or sexual forms. The nymphs, which at 

 first get less food and produce less exudation, receive less care 



