12 B. GRASSI AND A. SANDIAS. 



3. Numerous Protozoa were found in a few substitute kings 

 and queens of Calotermes which had been kept some days 

 in a glass jar containing a little wood^ together with many 

 other examples of the same species taken from different nests. 

 But during this time the royal specimens had been taken out 

 and put back several times^ and may be regarded as having 

 been disorganised. 



4. Lastly, a very few kings were found to contain a 

 moderate number of Protozoa in midwinter, — that is to say, at 

 a time very far removed from the period of copulation. 



Allowing all due weight to these exceptions, we may still 

 say that they are far from disproving, but rather confirm the 

 rule, which may be thus formulated: — "When the genital 

 organs are mature in individuals of which the wings 

 are not fully developed. Protozoa are absent, and the 

 dilated csecum is therefore of minimal size. The 

 absence of Protozoa does not, however, connote the 

 incapacity of the insects in question to possess them. 



But here a grave question presents itself. Is the absence of 

 Protozoa a cause of the ulterior development of the genital 

 organs, or simply a consequence ? Observations for the pur- 

 pose of solving this question were undertaken on comple- 

 mental or substitute forms in process of development (larvae or 

 immature examples). In these Protozoa were usually, but not 

 invariably, absent. The significance of this last fact is not 

 easily estimated, but after careful consideration I feel jus- 

 tified in offering the following explanation : — Examples in 

 process of becoming complementary or substitute sexual forms 

 do not habitually possess Protozoa; they may from time to 

 time become infected with them, but they rapidly get rid of 

 them independently of the moults. Possibly the development 

 of the genitalia is arrested during the infection. 



It follows from all this that in complemental and sub- 

 stitute forms there is an accelerated or anticipated 

 maturation of the genital organs which appears to 

 be in intimate relation with the loss of the parasitic 

 Protozoa from the caecum. Such a loss in growing 



