CADDIS-FLIES 



485 



Fig. 330. Oxyethira costalis. A, Larva 

 in case ; B, cases fastened to leaf for 

 pupation.. (After Klapalek.) 



of wings, while in Thamastes the posterior wings are absent in 



both sexes. These anomalies are 



at present quite inexplicable; and 



we may here mention that we 



are in complete ignorance as to 



the functional importance of 



many of the peculiarities of the 



Phryganeidae. We do not know 



why the moutli is reduced from 



the normal state, the maxillary 



palpi being, on the other hand, 



extraordinarily developed ; we do 



not know the importance of the 



numerous spines and of the 



spurs on the legs, nor of the 



hairs on the wdngs, although 



these are amongst the most 



characteristic of the special features of this group of Insects, 



Fossils. Abundant remains of Phryganeidae belonging to 

 the Tertiary epoch have been discovered. They are connnon in 

 amber, and it is a remarkable fact that a larval case has been 

 found in amber. This seems almost inexplicable, except on the 

 assumption that such larvae were of arboreal habits, a condition 

 that, at the present time, must be excessively rare, though the 

 terrestrial habits of Enoicyla warrant us in believing it may 

 occur. , In the Tertiary Lake Basin at Colorado the remains of 

 Phryganeidae in the imago state are extremely abundant, so 

 that it is curious that but few such remains have been found in 

 Europe.. In Auvergne the so-called indusial limestone, which 

 is two or three yards thick over a wide area, is considered to be 

 composed chiefly of the cases of larvae of this family. 



In the Mesozoic epoch some wings found in the lower Purbeck 

 strata are considered to be those of Phryganeidae ; similar wings 

 have been found in the Lias, but this is the only evidence of 

 the existence of the family at that period except a tube, supposed 

 to be a larval case, detected in the Cretaceous of Bohemia. 

 Earlier than this nothing has been discovered that can be 

 connected with the family, so tliat at present the palaeontological 

 evidence appears unfavourable to the view held by some that 

 the Phryganeidae may be considered forms allied to the early 



