( Ixviii ) 



The fiuiMnliiini is in Lepidoptera a small tiihcrclc aliove tlie pad between 

 the claws, bearing one bristle, seldom two. It is widely distributed among the 

 pad-bearing species, but is seldom found in Sphinyidae {Spliinguhis; Hopliocnema). 

 Tlie claws are simjjle in Sphiiigidae, not divided or toothed ; they are dilated at 

 the base (PI. XLIV.) The pnlvillns {piilr) varies much in size iu Lepidoptera, 

 and is often absent, the ])resence or absence freiiuently characterising genera and 

 whole subfamilies, but forming not rarely a distinction only of specific value. 

 Absence of the juiivillus is of common occurrence among Achcroiitiinae and 

 Ambullciixte ; while the organ is very seldom obliterated in the other subfamilies, 

 Arcto/wtus and Fjijiroserpiniis being the only instances. The jiaronychium {par) 

 is membranaceous, ventral and lateral in position, finely ciliated on the surface, 

 and provided «itli a more or less long fringe at the edges. Its special shape 

 varies much iu insects. It is generally deeply sinuate mesially, and each half 

 may be again divided (or perhaps produced) into two lobes. The })aronychinm 

 of Sphinqidac possesses in its most generalised state two slender lobes on each 

 side (PI. XLIV. f 9. 10), of which the upper (or lateral) lobe is generally the 

 longer, very rarely the shorter one. The reduction of the paronychium begins 

 with the ventral lobe (PI. LXIV. f 11. 12) ; this is always the first to disappear, 

 there being no Hawk Moths which possess the ventral lobe and are devoid of 

 the lateral one. The remaining lobe becomes also gradually shortened, and 

 disappears too, the ])aronychinm then being represented by a small ciliated 

 membrane, which is often less distinct than in f. 14. l-j of PI. LXIV. The 

 reduction and, practically, obliteration of the paronychium occur very often in 

 Aeherontiinae and AmhuUcinae, rarely in the^other subfamilies. Tlie difference 

 in the paronychium is often employed by us in the definition of genera. However, 

 there are genera {Ili/loicua) in which the absence or presence of a ])aronychial 

 lobe indicates only sjiecific distinctness, and sometimes not even that. Hi/loicits 

 perelegans consists of a black-backed and a grey-backed form, which are found 

 iu the same country, and are most likely seasonal forms. The black-backed form 

 possesses, like most other Ifi/loict/s, a long lateral lobe (PI. XLIV. f. 13), which 

 is represented in the grey-backed form by a short triangular flap (PI. LXIV. 

 i. 14. 15). This difference within the same sjiecies is of considerable significance. 

 The case teaches us distinctly that the same kind of character is by no means 

 everywhere of the same taxonomic value. No morphological character is a priori 

 of specific or generic value or indicates a higher category than genus. The 

 taxonomic value of a character has to be studied iu each group of s])ecies ; a 

 difference which is insignificant here may be very important there. 



The reduction of the claw-segment— or, rather, of the paronychium and pad, 

 for the claws never disapjiear, nor do they lose the ordinary shape— begins in 

 Spltingidae with the obliteration of the paronychial lobe. From this second 

 stage lead two paths to the abolition of the pulvillus and paronychium. The 

 ordinary ])alh is that on which the third stage is represented by a segment 

 without (or with strongly reduced) pulvillus, and with well-developed lateral 

 paronychial lobe ; while the fourth stage is attained when this lobe has also 



