EVIDENCE FROM MIMICRY. 155 



societies, the so-called animal communities a third group of indi- 

 viduals (sometimes even divided into several series of forms) which 

 are without generative organs and are incapable of reproduction, but 

 which assume the functions of protecting, of providing nourish- 

 ment for the community, and of caring for the young. Adaptive 

 peculiarities suitable for the discharge of these functions are 

 apparent in their structure and organization. These sterile indivi- 

 duals are in the Hymenoptera aborted females. Among the ants 

 they are divided into workers and soldiers. Amongst the Termites 

 they are derived from both males and females, in which the genera- 

 tive organs are reduced. Sterile individuals are also found amongst 

 animals (Fishes) which do not form communities, and were formerly 

 taken for particular species and described as such. Polymorphism is 

 most highly developed in the Hydroids which are united in stocks 

 the Siplwnopliora. 



The numerous cases of dimorphism and polymorphism in either 

 sex of the same species, should be regarded from the same point of 

 view. Dimorphic females among insects have been observed, e.g., in 

 the Malayan Papilionidce (P. Memnon, Pamnon, Ormenus), in cer- 

 tain species of Hydroporus and Dytiscus, as also in the Neurotemis, a 

 genus of the Neuroptera. In these cases, as a rule, one of the 

 female forms is more nearly related in form and colour to the male 

 form whose peculiarities it has assumed. In other cases the 

 differences are more connected with climate and season (seasonal 

 dimorphism of butterflies), and also affect the male animal. They 

 may be connected with the different forms of reproduction (parthen- 

 ogenesis), and lead to the phenomenon of heterogamy (Chermes 

 Phylloxera, Aphis). Much more rarely we find two kinds of males 

 with dissimilar secondary sexual characters connected with copula- 

 tion, as in the case of the " smellers" and " claspers " * described by 

 Fritz Miiller in the Isopoda (Tanais dubius). 



Evidence from Mimicry. Another series of phenomena which 

 -may probably be referred to useful adaptation is the so-called 

 mimicry. Certain animal forms come to resemble other widely- 

 distributed species, which are protected by any peculiarity of 

 form and colour, so closely that they seem to have copied them. 

 The cases of mimicry which have been principally made known by 

 Bates and Wallace are directly connected with the protective 

 resemblances mentioned above; that is, the resemblance of many 

 animals in colour and body shape to the objects amongst which they 

 * Fritz Miiller, " Facts for Darwin," p. 22. 



