WINGLESS REPRODUCTIVE TYPE OF TERMITES 605 
between these two castes suggested at first, as stated in the 
introduction, that the third-form adult might be merely a physio- 
logical phase of the worker caste or, in other words, a fertile 
worker. The infrequent occurrence of the third-form adults 
might indicate, it was thought, that occasionally a worker 
nymph would revert to its probable ancestral condition of 
9 
Fig.9 Reticulitermes flavipes. Third-form adult, female, optical section of 
head. 
Fig. 10 Reticulitermes flavipes. Worker, adult, optical section of head. 
br, brain; c.e, compound eye; f.g, frontal gland; oc, ocellus. Spencer oc. 6, obj. 
16 mm., table level, reduced one-third. 
fertility, as in ants and bees, developing into the rare and fertile 
third-form adult; the majority of the worker nymphs, however, 
developing into sterile workers. A careful comparison of the 
two castes in question proves beyond doubt that there are here 
two distinct castes, biologically, morphologically, and physio- 
logically different, and that the superficial resemblance is more 
than counterbalanced by the many minute structural differences 
revealed by the study of whole mounts and sections. 
