309 



the specimens combine the characters of at least two different species, 

 without being- referable to either, satisfactorily, and in the present state 

 of onr knowledge most entomologists would be justified in describing- 

 them as distinct species; but there can be little doubt that when abun- 

 dant material from different localities is obtained all these transversely- 

 marked forms will be difficult to separate. Such, however, is the case 

 in almost every genus, whether of plants or animals, and the Prodoxids 

 simply furnish us with a rather marked illustration of the fact that the 

 variation has gone on and is going on, so far as purely colorational 

 characters are concerned, without any very definite and unchangeable 

 differences having yet been acquired. How strikingly such facts com- 

 pare with the permanency, even in colorational characters, of such well- 

 established species in the same order as the cosmopolitan Vanessa car- 

 dtii, which, with a most beautiful wing design and a most complex col- 

 orational pattern on the inferior surfaces, remains essentially constant 

 in all its details in all parts of the world where it is known ! 



The decurved hooks in the larva; of Prodoxus cinereus are also 

 most interesting- from an evolutional point of view. Such anal hooks 

 are extremely rare in Lepidopterous larv;e, being- found in only a very 

 few pith-boring or stem-boring species.* 



We have in this structure, which is so exceptional in Lepidoptera, 

 another illustration of a principle to which I have often referred in my 

 writings, namely, that larval structure in insects has been modified 

 independently of the ultimate structure and is, as a consequence, of 

 very little taxonomic value. Thus we have in the same family the 

 larviie of a Prodoxus {e. //., the typical decipiens), which remain in their 

 short burrows, possessing no legs; while those of Pronuba, which quit 

 their burrows and penetrate the ground, possess thoracic legs. Yet in 

 the particular case of Prodoxus cinereus the larva apj)roaches Pronuba 

 in having thoracic tubercles which may be looked upon as either rem- 

 nants of legs or the beginnings of the development nf such. This larva 

 burrows in the soft pith of Yucca ivhipplel much more freely than any 

 of the other species of the genus so far studied, making much longer 



* I have not had time to closely scan the literature for cases of this kind, but do 

 not recall any. I am familiar, however, with three unrecorded instances, two of 

 them of Pterophorid larvae which bore the stems of Solidago. One is the larva of 

 AlucUa kellicollii Fish, which singularly de^jarts from the typical Lepidopterous 

 larva in its elongated body and in having a pair of suj)ra-anal spines which give the 

 anal plate an appearance characteristic of that of many Coleopterous larva". The 

 second case is that of an undescribed species of the same family Pterophoridie, which 

 has the anal plate oblicinely truncate and fringed with a row of stiff hairs, and with 

 a pair of small thorns at its ventral border, this modification also recalling that 

 possessed by several wood-boriug Coleopterous larvie. The third case is that of the 

 larva of a Noctuid, Hadena stipata Morr., which burrows in the pith of young corn or 

 maize. It has the anal plate obliquely truncate and flattened along the posterior 

 margin, which is armed with a series of horny points, and thus again repeats the 

 structure whicli recurs in certain Coleopterous larvaj, especially of the Elateridpe., 

 which inhabit burrows in the trunks of trees. 



