. ORIGIN OF CASTES OF TERMITES 89 



and, at need, may be made into the 'substitute' or 'comple- 

 mental' royal forms. The chief factor in differentiation is 

 thought to be nutrition, the amount and quahty of the food 

 determining the large and small headed nymphs and from them 

 the adult castes^. The presence or absence of parasitic protozoa 

 in the alimentary tract and their inhibiting effect upon the 

 developing sex organs of the workers and soldiers is regarded as 

 a secondary factor, which itself may be affected by the quahty 

 of the food. In other words, the food, 'saliva,' administered to 

 those 'larvae' which are to become sexual forms, has the prop- 

 erty of destroying the protozoa which may enter the intestine; 

 the food of the 'larvae' to become workers and soldiers permits 

 the intestinal protozoa to live, and in some way the protozoa 

 check the growth of the developing sex organs. 



The following quotations will serve as a further exposition of 

 Grassi's view. 



The gonads are sexually differentiated, and the vasa deferentia and 

 oviducts are present at the time of birth, but there is no trace of the 

 external genitalia, which do not become evident until the larvae are 



divisible by the greater or less size of the head Newly 



born larvae receive nothing but saliva, but little or none is administered 



later to those in progress of becoming workers or soldiers 



A large amount of saliva is administered to examples destined to 

 become neoteinic; it causes the disappearance of the parasitic Protozoa. 

 The importance of this disappearance is not clearly understood, but 



it is certainly insufficient by itself to produce neoteinia 



Although details cannot be given it may be concluded that the de- 

 velopment 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 constant pre sence in great numbers. 

 The method by which the soldier is further differentiated 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 is one of nutrition. 



Emery, in various writings upon the polymorphism of social 

 insects ('93, '96, '04, '10) advances a peculiar view which seems 

 like a special modification of Weismann's theory. Emery 



* Grassi, distinguishes three kinds of fertile adults; 'perfect insects,' 'substi- 

 tute' or 'neoteinic' forms, 'complemental' forms. 



