30 B. GRASSI AND A. SANDIAS. 



tined to become workers and soldiers, or the latter 

 alone in Calotermes, in which workers do not exist. 



Although details cannot be given, it may be concluded that 

 the development of the soldiers and workers is consequent on 

 the less quantity of saliva which they receive ; and with this 

 is associated the earlier appearance of Protozoa, and their con- 

 stant presence in great abundance. 



The method by which the soldier is further diflferentiated 

 from the worker is a more obscure matter to determine. Is 

 the larger amount of nutriment which the latter receives the 

 cause of such a phenomenon ? In any case it is certain that 

 the essential factor must be one of nutrition. 



Numerous experiments have shown that the soldiers cannot 

 become royal substitutes, and further that they themselves 

 are incapable of transforming larvse or suitable nymphs into 

 substitute forms. 



General Considerations and Retrospective Note on 



Thysanura.^ 



1. The soldiers, workers, neoteinic forms (complementary 

 or substitute kings and queens), and the true perfect insects 

 are all derived from similar ova ; in other words, every ovum 

 must be regarded as inherently capable of giving rise to any 

 one of these four classes of forms. It follows that the dif- 

 ferences between them connote something absolutely unrelated 

 to the distinctions of sex; and the existence of Termite 

 castes has therefore no bearing on the theory which 

 postulates that every somatic cell is derived partly 

 from the mother and partly from the father. 



The following points are also of importance : 



(1) The neoteinia of Termitidse is no isolated phenomenon, 

 but is paralleled in many other insects, including the Orthoptera 

 (sensu lato). 



Sexually mature forms, some with well-developed, others 

 with short wings, and that independently of sex, are met with 



1 [Grassi, ' Atti Ace. Lincei' (4), iv (1887), pp. 543—606, pis. i— v ; with 

 bibliography of the author's antecedent memoirs on Thysauura.] 



