278 AN INTRODUCTION TO ENTOMOLOGY 



this differentiation takes 'place later as the result of extrinsic factors, 

 such as food, the presence or absence of parasitic protozoa in the 

 alimentary tract, and the care received from the older workers. 

 According to the second view the yoiing of the different castes are 

 different and the castes are therefore "predetermined in the egg or 

 embryo by intrinsic factors." 



Some comparatively recent investigations support the second view. 

 It was foimd by Thompson ('17 and '19) that although the newly 

 hatched nymphs are externally all alike, they are differentiated by 

 internal structural characters into two clearly defined types: first, 

 the reproductive or fertile forms, with large brain and large sex organs, 

 and usually a dense opaque body; and second, the worker-soldier or 

 sterile forms, with small brain and small sex organs, and usually a 

 clear transparent body. 



It was also fovmd by Thompson that later, when the nymphs had 

 become from 2 mm. to 3 mm. in length, they were differentiated into 

 "small-headed" but large-brained reproductive forms, and "large- 

 headed" but small-brained worker-soldier forms. In the case of 

 worker-soldier nymphs of Eutermes pilifrous, a Jamaican species, which 

 were 2 nun. long and externally all alike, they were distinguishable, 

 after staining, into worker nymphs with a small vestigial frontal 

 gland, and soldier nymphs with a large frontal gland. 



In a study oi Reticulitermes (Leiicotermes)fiavipes , Thompson ('17) 

 fotmd that the n3miphs of the reproductive forms that are only 1.3 

 to 1.4 mm. in length are differentiated into two groups by differences 

 in the size of the brain and sex organs. These are early instars of 

 the first reproductive caste and the second reproductive caste, respec- 

 tively. The early instars of the third reproductive caste have not 

 been distinguished from the nymphs of workers. 



There is space here for but little regarding the nest-building habits 

 of these wonderful insects. In the tropics certain species build nests 

 of great size. Some of these are mounds ten or twelve feet or more 

 in height. Other species build large globular masses upon the trunks 

 or branches of trees or upon other objects. Figure 315 represents 

 such a nest which I observed on a fence in Cuba. Owing to the 

 delicacy of their cuticula and the consequent danger of becoming 

 shriveled if exposed, the termites build covered ways from their 

 nests to such places as they wish to visit, if they are in exposed 

 situations like that shown in the figure. These exposed nests are 

 composed chiefly of the excreted imdigested wood upon which the 

 insects have fed. This is molded into the desired form and on drying 

 it becomes solid. 



The termites that live in the United States do not build exposed 

 nests; and, as the queens do not lose the power of movement, there 

 is no permanent royal cell, centrally located, in which the king and 

 queen are imprisoned, as is the case with many tropical species. 

 Some of our species mine in the earth, their nests being made under 

 stones or other objects lying on the ground; some burrow only in 



