8 PACKARD, NOTES ON THE 



York ; F. W. Putnam, who collected the larvae and pupae of 

 Eudryas grata, in alcohol at Bridport, Vt., which are now in 

 the collection of the Museum of Comparative Zoology at Cam- 

 bridge ; and for specimens of Castnia to the collection of the 

 Essex Institute. 



Besides the interest excited by the discovery of the transfor- 

 mation of any member of this family of moths, the near rela- 

 tionship of Ctenucha to the Bombycidae attracts our attention. 

 This genus when in the larval stage, so closely resembles the 

 Arctians, as to have misled us wholly as to its nature upon 

 first meeting with it. Indeed we were convinced that we had 

 found a larva of Pliragmatobia rubricosa Saunders and were 

 much surprised at raising Ctenucha from it. On the other 

 hand the moth has been referred by Walker to the Lithosiidae. 

 Here we see such u delicate balancing of analogical and struc- 

 tural features, that different writers do not agree which natural 

 group to refer the object to. Thus those who place Ctenucha 

 among the Lithosians (the highest sub-family of Bombycidae) 

 think of course, that the Zygaenid characters which the moth 

 possesses are those of analogy, while those of a contrary mind 

 judge the same moth to be a Zygaenid with the less essential 

 features borrowed from the Bombycidae. This leads us to 

 the enquiry, how far analogy differs from affinity. It is evident 

 that the relation is only rel.itive and not absolute. Typical 

 animals are those having the greatest mass ot characters to 

 isolate them from others For instance, among the Zygaenidae, 

 the Fabrician genus Zygsena is the type of the family, just as 

 in the Bombycidae, Telea Polyphemus Hiibner, or. still better, 

 Attacus Atlas Linn, are the types of that family. In Zygcena 

 we have forms the most unlike other genera of its family. 

 There is not a character drawn from its structure or habits 

 which is not sui generis, original, unique. It is the pattern 

 upon which the family form is moulded, and the moment the 

 form is slightly modified, and any resemblance to some other 

 moth is superadded, as in Syntomis which already begins to 

 show Lithosian affinities, that moment something has gone from 

 it. There is a loss in affinity, and what is thrown in to supply 

 the vacancy is a gain in analogy. 



In the genus Attacus we have massed together a number of 

 characters which are those of pure affinity (using the term in 

 its technical sense, otherwise it has no meaning in specifying 



