530 JO UNA L, BOMB A Y NAT URAL HISTOR Y SOCIE T Y, Vol. XI. 



His conclusions were supported by observations in nature, but were not 

 made the subject of experiment ; they are to be regarded as suggestions, 

 which, however, approach very nearly to the truth. 



The subject was taken up by Prof. Grassi in order to investigate the origin 

 of the sterile castes, and the results of seven years 1 labour have been put 

 forward in a monograph which, for the first time, places the nature of the 

 termite society beyond the reach of speculation. Intricate as the memoir is 

 in the presentation of facts and inferences, it cannot but leave the reader 

 with a profound sense of the perseverance, fertility in experiment, and 

 deductive ability which it reveals. 



Species of two genera, Calofermes and Termes were studied, and success 

 was largely due to the fact that it was found possible to keep small numbers 

 of the f firmer genus alive for long periods in corked test-tubes containing 

 rotten wood. Careful observation thus became practicable, and by varying 

 the number and kind of individuals introduced, their development and inter- 

 relations could be studied. 



Grassi's work on Calotermes shows that the eggs are of one kind and the 

 newly-hatched larvae undifferentiated, the caste distinctions arising after 

 birth, and depending on the development of the genitalia. If this process 

 normally, the larva ultimately becomes a winged imago ; if it is arrested at 

 any period before the completion of the nymph-stage, the larva becomes a 

 soldier ; and finally, if it is precociously stimulated, a neoteinic form is 

 produced, one, that is, which reaches sexual maturity without ever acquiring 

 the imaginal characters. The insect remains plastic until the atrophic change 

 of the genitalia has been set up ; thus a soldier-larva or soldier cannot be 

 modified, but a nymph can be converted into a soldier possessing wing-buds 

 (a " nymph-soldier "). These buds may be subsequently reabsorbed, so that 

 a retrogression actually takes place. The colony is headed normally by a 

 single king and queen derived from the perfect insects ; should either or both 

 be missing, their place is supplied by neoteinic " substitute " forms, which are 

 then always produced if the society contains examples capable of undergoing 

 this modification. An orphaned colony may be made to produce a much 

 larger number of substitutes if subdivided into small societies than if kept 

 together, and the same is true of the soldiers. This and similar observations 

 go clearly to show that the modification of these individuals is in no way 

 predestined. 



The insects must possess the faculty for estimating a numerical ratio, and 

 if the number of soliders or royal substitutes is in excebs of their needs, the 

 supernumeraries are killed and eaten ! 



The colony of Termes is more complex and more difficult to study : it is 

 similar in character except that it contains two sterile castes, soldiers and 

 workers, and two kinds of neoteinic forms, one, the " complementary royal 

 forms, " are constantly present in large numbers as the ordinary reproductive 



