( 401 ) 



became scales had been re-acqnired — an asanmption which I do not admit — the 

 occurrence of antennae covered all over with sense-hairs is intelligible only if the 

 ancestral antenna was of a similar type. Hence we have to regard the antennae 

 differing from that ancestral type of the whole order as specialisations into which 

 tlie ancestral form of antenna has developed, and now come to the qnestion, whether 

 the Batterfly antennae are directly derived from this most primitive type or from 

 a later development of it, and whether the varions Butterfly antennae developed 

 independently of those of the Moths and independently of one another (in respect to 

 scaling). 



In all Butterflies and Moths, with the exception of some .Tugatae, the dorsal 

 and ventral sides of the antennae are different in respect to the development of 

 sense-hairs and scaling ; these antennae are, therefore, all more or less specialised. 

 But the different degrees of specialisation met with in Butterflies show us clearly 

 from what kind of ancestral antenna the various Butterfly antennae must have 

 developed. The ventral side is in very many species of all Butterfly families, 

 except Hesperiidae, covered all over with fine sense-hairs, and the same character 

 obtains on the upperside of the distal joints in many Lt/cfienidar. Hence it is 

 evident that we must attribute to the original stock of Lopidoptera, from which the 

 Butterflies developed, antennae very similar in the development of fine sense-hairs 

 to those of the ancestor of the whole order, but perhaps with a more or less 

 extended dorsal scaling. 



In the further development of this ancestral antenna the dorsal and ventral 

 side did not lose the generalised character at the same time, both aides deviating 

 markedly from each other. From the facts, firstly, that in many Butterflies and 

 nearly all Moths the ancestral covering of fine sense-hairs is still present on the 

 ventral side, while the dorsal side is in nearly all Lepidoptera specialised, and, 

 secondly, that in the species in which l)oth sides are specialised the sensory hairs are 

 more restricted dorsally than ventrally, the ventral side never being in advance over 

 the dorsal surface in this respect, we are justified in inferring that the modification of 

 the sensory hairs began on the dorsal side. As further the ancestral character of a 

 covering of fine sense-hairs is ke])t in many Lycacnidue on the dorsal surface of the 

 distal joints, while the rest of the dorsal surface is densely scaled, and the dorsal 

 not-scaled area is alwaj's distal in all Butterflies, if the dorsal side is not totally 

 covered with scales, the development of the scaling must have set in at the base and 

 proceeded in a basi-apical direction, so that the totally scaled dorsal surface is a 

 later acquirement. The gradual modification of tlie sensory hairs into scales in 

 a basi-ai)ical direction is beautifully illustrated in .Tugat(u\ where we find all inter- 

 gradations between antennae with totally hairy and totally scaled dorsal side, the 

 not-scaled portion preserving the generalised character. 



The acquirement of extended dorsal scaling is not always the end of this lino 

 of development. Those many species which are closely related to species with 

 extended antennal scaling, bnt have neither scales nor sensory hairs on the dorsal 

 side of the antennae, and hence are not of a more ancestral tj-pe, clearly show that 

 their dorsally naked antenna is a derivation from a scaled one. There are a. priori 

 two ways u])on wliich the antenna can have arrived at this stage of development. 

 The first possibility is that the fully scaled area became restricted gradually in an 

 apici-basal direction without a reduction in the number and size of the scales of the 

 rest of the area, retracing backwards the steps of develojiment which originally led 

 to an extended scaling. But the intergraduatc stages between tiie not-scaled and 



