MEMBRA Cl DM. 
151 
Life is the tie which controls, varies, and binds organisms within definite channels 
and lines of development. Such phenomena result in variation, which phenomena 
however are checked by the energies at work necessary to secure the historical, it not 
the absolute, fixity of species. Without these first conditions, the science of zoology 
could not be debated. 
It has been argued that variety shows itself by synthesis or accretion of parts of an 
organ more or less useful, or the analysis or suppression of forms which finally are 
atrophied as not beneficial to the animal. There may be also an abeyance for want 
of the presence of a suitable stimulus. 
It is out of the scope of this monograph to attempt a discussion of the views of 
Galton, Weismann, and others, as to the bearing of heredity on variation or, on the 
other hand, those of Wallace, Herbert Spencer, and Semper. Well ascertained facts 
are the province of a classificatory treatise. Correct deductions from such facts will 
come best from the materials furnished and the reader’s private judgment. 
Struggle for the fittest will account for much variation on certain lines of utility. 
The protected must have advantages over the unprotected. However, the biologist 
has to show what are the adverse causes which are detrimental to an animal’s 
economy, and how mimicry amongst other devices is an efficient protection. 
It is asserted that all animals in a state of nature have their organs in such a 
state of super-abundant vigour that in cases of difficulty or necessity they can draw 
upon this overplus. 
How far this power is under the conscious will of the animal is questionable, and 
how far it is checked by instinctive action. Means provided for the accomplishment 
of a definite purpose seem to point to design, unless we assume the clumsy expedient 
of a resort to blind law or necessity. 
Students of the family of Membracidse are under difficulties as to the explanation 
of mimicry, for at present they are ignorant of the natural enemies of the group. 
Vegetable mimicry by animals may be protective, but not aggressive. Thus the 
genera of Sphongophorus, Bolbonota, and Pterygia simulate barks of trees, either 
as gnarled, smooth, grey, green, or lichen coloured. Umbonia, Triquetra, and some 
Centrotidae appear, more or less, thorny like the acacia, prickly like the bramble and 
rose, or finely spined like the stinging hairs of the nettle. Such are vegetable 
representatives of the family. 
When we come to the mimicry of animals the problem becomes more complex, for 
we must here learn or guess what are the foes against which protection is sought. 
The genus Harnis and Stictopelta resemble shining gramineous seeds, or else small 
shining slugs, which can hardly be protective against birds. The imitative faculty 
is well shown in the bee-forms of Hoplophora, whilst in Heteronotus and Combophora 
