584 CAROLINE B. THOMPSON 



In the two n>Tiiphs with long and short wing pads the frontal 

 gland seems not yet functional. There is no external opening 

 above the gland; the cells which appear capable of producing 

 secretion are few and scattered, while most of the cells are nar- 

 row and slender with no evidence of any contained secretion, 

 but resembling rather sensory cells in their form and contents. 

 The last nymphal molt will remove the outer cuticula, and the 

 absence of the inner cuticula, described above, will produce the 

 external opening seen in the true adult. At the same time the 

 epithelial cells which were not glandular in the nymphal phases 

 may form a cuticula on their inner surface, acquire the power 

 of secretion, and become fully glandular in function in the adult 

 condition. It would therefore seem that the frontal gland of 

 nymphs with long and short wing pads represents an earher 

 phase of development than that of the true adult or soldier. On 

 the other hand, it is apparent that the frontal gland of the 

 worker is in a secondarily modified and regressive condition. 

 It is evidently nonfunctional, the cells showing no signs of secre- 

 tion; it is also degenerate in structure, for the cells, although of 

 the same form as in the nymphs, are much smaller, are numeri- 

 cally fewer, and are partly replaced by a network of mesenchym. 



The study of the frontal gland might end here with the fre- 

 quently asked and still unanswered question : What is the function 

 of the frontal gland? The question, however, that has presented 

 itself most forcibly throughout my study of this organ is. Why 

 should most of the epithelial cells of the frontal gland in the 

 nymphal phases bear such a striking, resemblance to sensory 

 cells? Young gland cells may usually be recognized as such 

 even in their early phases, and they are rarely so slender and 

 elongated. If, as the biogenetic law teaches us, ancestral struc- 

 ture is frequently to be observed in young, that is, in develop- 

 ing organs, is this then an instance? It is possible that the 

 frontal gland of the termite, whose function is unknown and 

 whose structure needs further investigation, may represent an 

 ancestral organ, highly developed and secondarily modified in 

 some individuals and vestigeal in others, but whose primitive 



