90 CAROLINE BURLING THOMPSON 



believes that the distinctive characters of the castes of social 

 insects are present in all eggs, not as determinants, but as special 

 sensitive conditions of the germ plasm, which manifest them- 

 selves only under specific external conditions or with specific 

 stimuli. The quality and the quantity of the food are important 

 stimuli and indirectly produce differentiation. "Senza dubbio 

 si regola I'evoluzione individuale delle Termiti con mezzi che 

 sono, almeno in massina parte, dietetici, ma non sappiamo 

 quali." 



Silvestri ('02, '03) holds the view that food is the determining 

 factor in caste differentiation, although an indirect factor, since 

 the germ plasm is also involved. He writes : 



Abbiamo visto che le uova delle Termiti sono tutte iiguali fra di 

 loro e che da esse, a volonta degli operai, per mezzo di una speciale 

 nutrizione si possono svillupare o individui alati o operai o soldati, 

 quindi I'idioplasma di ciasc.un uovo sotto lo stimolo di un cibo diverso 

 e capace di reagire diversamente : di far svilluppare alcuni caratteri 

 somatici ed altri arrestarne. Cio e ormai un fatto accertato per tutti 

 gli insetti sociali e non si pu6 intorno ad esso sollevare dubbio di sorta. 



La questione sta nel come I'idioplasma di un uova di Termitide 

 possiede anche i germi dei caratteri di operai e soldati una volta che 

 esso e generato da individui sessuati con alcuni caratteri affatto diversi 

 da quelli degli operai e soldati, che sono sterili. 



Heath ('03) studied the habits of three California termites, 

 Termopsis angusticollis, Calotermes castaneus, and Termes 

 (Leucotermes) lucifugus, and makes the following general state- 

 ment regarding the origin of the castes : 



It is now thoroughly well established that the soldier and worker 

 in the termite colony are not the result of the arrested development of 

 the reproductive organs. It has also been shown that they are not 

 restricted to either sex. And it is almost equally certain that their 

 differentiation is not to be traced back to the newly hatched young. 

 The latter, when they first appear are exactly alike in form and color, 

 though they may exhibit slight differences in size, and the characteristics 

 of the different castes develop at varying times after the first molt. 

 If then neither arrested development, nor sex nor heredity are directly 

 responsible for the production of soldiers and workers, what is the agency 

 immediately concerned? Grassi is of the opinion that it is the food. 

 Owing to its character or amount or both, the royal pairs of the colony 

 are able to transform the larvae into soldiers, workers or perfect in- 

 sects For months I have fed a large number of termite 



