In any case, whether we can discover them or not, some curious points of difference must exist between this spider and its allies, which secure to it a comparative immunity. It appears to me that there are few questions which can be of greater interest to the naturalist than those which have to do with the conditions determining the existence of a given species in a given place. Of the questions, Who are your relatives? Where do they live? and How are you able to live here? surely the last is not the least important. And, if we wish to try to answer this question, we must do all in our power to find out how the habits and conditions of life of the creature in question, differ from those of its competitors; for we may be quite certain that it does not exist where we see it by grace and favour, but by merit; if it is neither stronger, cleverer nor more numerous than its neighbours, we may be sure that it has found some means of living which does not interfere fatally with their requirements. Hence the endless diversity of function and habits in all living creatures, which forms such a prolific and marvellous subject for our study and contemplation. I am indebted to M. Simon for permission to publish the details given above on _Cyrtauchenius elongatus_, and also for having given me such directions as enabled me to make the sketch from which the drawing at Plate XIII., fig. B, was copied. I must however state that this illustration is not taken from an actual specimen, but is prepared solely from his description; so that it cannot pretend to complete accuracy of detail. M. Simon assured me nevertheless that it conveyed the general appearance of this remarkable nest with sufficient fidelity, and I have been induced to reproduce it here in the hope that it may serve to make my meaning plainer, and to suggest the kind of object which one should look for, if an opportunity offered. Another species of the same genus, _Cyrtauchenius Doleschallii_, is known to inhabit Sicily, but the nest is undescribed. M. Lucas has described two species,[129] belonging to the closely-allied genus _Cyrtocephalus_, both of which appear to construct nests somewhat similar in form to that discovered by M. Simon. Whether these nests are equally showy we cannot tell, as the account is brief and few details are given; but one, that of _Cyrtocephalus terricola_, appears to differ in having threads stretched from the opening of its funnel, which serve to ensnare insects and to give notice of these captures. [Footnote 129: _Cyrtocephalus Walckenaëri_ and _terricola_, Lucas (H.), _Animaux articulés de l'Algérie_ (Paris, 1847-9), vol. i. p. 94-5.]