88 CAROLINE BURLING THOMPSON 



Herbert Spencer ('93-'94) in his controversy with Weismann, 

 defended, as is well known, the inheritance of acquired characters, 

 and, as a logical consequence, believed in the direct action of 

 food and environment upon the body. In regard to the origin 

 of the castes of social insects Spencer held that: 



the different structures of queen and workers are determinable by differ- 

 ences of feeding. Therefore the production of their different castes 

 does not result from the natural selection of varying germ plasm. 



A work which has been very widely read and quoted, and which 

 has exerted an influence, probably greater than any other, upon 

 biologists' views of the origin of termite castes, is a monograph 

 by Grassi ('93-' 94) in collaboration with A. Sandias. This 

 monograph was translated by Blandford and published in '96- 

 '97; the quotations here given are from the translation. 



In his introduction Grassi states that the elucidation of the 

 origin of castes in termites is of the highest interest, since it 

 involves the theory of evolution, the question of the inheritance 

 of acquired characters, and the constitution of the soma and 

 germ plasm. His interest has been aroused by the study of 

 bees, where nutrition apparently has a great influence upon the 

 sex organs, which 



would indicate that the environment has a powerful and direct influence 

 upon the genitalia, and would therefore tend indirectly to show that the 

 much disputed inheritance of acquired characteristics is a possibility. 



The work deals with the habits, structure, and development 

 of two termites, Calotermes flavicollis Fabr., and Termes (Leu- 

 cotermes) lucifugus Rossi. The following is a brief statement 

 of Grassi' s observations and conclusions upon the origin of ter- 

 mite castes. 



The newly hatched 'larvae,' 1 mm. long, are all alike, or un- 

 differentiated; by the time they have attained a length of 2 mm. 

 two types may be distinguished, with large and small heads 

 respectively. From the 'large headed larvae' the sterile workers 

 and soldiers develop; the 'small headed larvae' give rise to the 

 reproductive forms and also to some sterile forms. Some 

 'undifferentiated larvae' are always kept in reserve by the colony, 



