418 Mr. Westwood's Illustrations of the 



prevents a positive assertion upon this point*. The variations, however, ex- 

 isting between these two groups in the important organs noticed above is so 

 great, that, in comparison with the structure of other allied tribes, it must be 

 admitted that we here find the real characteristics of an analogy, namely, ex- 

 ternal similarity of form, but a complete diversity of structure in the essential 

 organs. 



The examples hitherto produced have exhibited analogies existing between 

 insects belonging to the same order. In this latter respect, however, (or, in 

 other words, on account of their Coleopterous structure,) they are related 

 together by affinity. 



Of the still more widely extended relationship resulting from analogy, many 

 examples might be given. Some have already been noticed in the introductory 

 remarks upon the genus Diopsis, published in the last volume of the Trans- 

 actions of this Society. Others may be mentioned wherein a great enlargement 

 either of the scutellum or the posterior part of the prothorax is observed, 

 which, contrary to the ordinary structure, is extended entirely over the body 

 and wings. The genus Scutellera (so named from this circumstance) amongst 

 the Heteropterous Hemiptera, many Centroti, &c. amongst the Homopterous 

 Hemiptera, the species of Acrydium (I'etrix, Latr.) in the order Orthoptera, 

 Thorocantha, Latr., in the Hymenoptera, and Celyphus, Dalm. in the Diptera, 

 — respectively exhibit this singularity of formation. 



The curious genus Copium, Thunberg {Holhymenia, Serv. and St. Farg.), is 

 strikingly represented amongst Dipterous insects by the insect which I have 

 figured in Griffiths's "Animal Kingdom" under the name of Diateina Holhyme- 

 nioides, and in which the structure of the antennae, and even the white colour 

 of the terminal joints, are especially traceable in a most singular manner. 



The Neuropterous genus Ascalaphtis in like manner analogically represents 

 the genus Papilio in another Order, Lepidoptera. But the most complete 

 instance which I have hitherto met with, of deception produced by an insect 

 of one order assuming the appearance of another, occurs in the species about 



* P.S. The recent discovery by Dr. Ratzeburg of the larva of Bostrichus capucinus fully confirms my 

 supposition, it being hexapod, whilst that of the Scolytidee is apod. Thus whilst the antennae, trophi, 

 tarsi and larvse of Rhyzopertha and Tomicus are totally distinct, their general form and habits are simi- 

 lar, thus establishing their relation as one merely of analogy. 



