126 CAROLINE BURLING THOMPSON 



F. THE QUESTION OF THE ORIGIN OF THE THIRD REPRODUCTIVE 

 CASTE, WITH NO WING PADS, IN L. FLAVIPES 



No evidences whatever of a prototype for the third reproductive 

 caste of L. flavipes have yet been observed in this study of 

 development. 



It will be recalled (Thompson, '16, and Snyder, '15 and '16), 

 that the third reproductive caste is entirely wingless, having 

 neither wings nor wing pads. This form is of rare and infrequent 

 occurrence in the genus Leucotermes and practically nothing is 

 known of its internal structure. Mr. Snyder has permitted me to 

 quote his statement that he has found only five queens of this 

 caste in the genus Leucotermes — three in L. flavipes, one in 

 L. virginicus, and one in a new species — and that he knows of no 

 record of others having been found in the United States. 



DISCUSSION AND CONCLUSIONS 



That the newly hatched nymphs, although externally all 

 alike, are internally differentiated into two distinct types of 

 individuals proves, first, that these types are predetermined at 

 the time of hatching, and second, that the two generalized types 

 of reproductive individuals and worker-soldier individuals are 

 fundamentally different. There can be no question of changing 

 one type into the other; each, from the beginning, is a distinct 

 entity with sharply defined morphological characters. 



The conversion of the 'undifferentiated' nymphs, by feeding, 

 into large and small headed forms, and these again into the future 

 adult castes; the production of 'substitute' reproductive forms 

 from an ever present 'reserve' of 'indifferent larvae,' or by the 

 alteration of forms whose development has already begun; 

 the sudden and opportune appearance of 'substitute' forms in 

 'orphaned' nests; all these assumptions, which, indeed, appeal 

 to our sense of the dramatic and marvellous, must now be re- 

 garded as possessing chiefly an historic interest. 



The later differentiation of the generalized reproductive type, 

 when it has attained a length of 1.3 mm., into the prototypes 

 of two of the specialized adult reproductive castes results finally 



