78 ILLINOIS BIOLOGICAL MONOGRjiPIIS (320 



locomotion, <an advantage which is greater in the earlier inslars than in the 

 later, especially with noctuid larvae of the ground and subterranean strata. 

 This factor of unequal function in different inslars has completely obscured 

 the effects of recapitulation, as in the parallel situation of the unequal 

 function of the spinneret, which has been previously discussed. Thus 

 additional support is given to the law stated to the effect than unequal 

 function is dominant over recapitulation when these factors act in opposi- 

 tion to one another. 



Henneguy states that the gaining of the first pair of larvapods occurs 

 during postembryonic development in the European noctuids, Agrolis 

 pronuba, (Agrotinae), Polia nebttlosa (Hadeninae) and Trachea atriplicis 

 (Acronyctinae). This condition has been found by the author in Agrotis 

 ypsilon and in Fellia suhgothica, altho the first pair of larvapods is fairly 

 well developed in the first instars of Agrolis c-nigriim and badinodis. In 

 Lycophotia margarilosa, of the same subfamily, they are present but ex- 

 tremely vestigial, bearing only two or three crochets. A similar difference 

 with respect to this point is also found in the genus Polia. The American 

 renigera has the first pair of larvapods comparatively well developed in the 

 first stadium, as does the rather closely related Ceramica picla, whereas 

 they are reported absent in the European Polia nebulosa. In like manner 

 they are not strikingly smaller than the second pair in the newly hatched 

 larvae of Sidemia devastatrix, altho Henneguy states that they are absent 

 in those of the closely related Trachea atriplicis. 



The difference in the development of the first pair of larvapods in 

 closely related species indicates that this developmental character is not a 

 fundamental one from the taxonomic point of view. The scattered occur- 

 rence of their absence in the first two stadia thruout the subfamilies 

 Agrotinae, Hadeninae, and Acronyctinae shows that this condition, like 

 the length of the epicranial stem and like the number of molts, has origi- 

 nated independently in different species. The tendency toward the reduc- 

 tion of the first two pairs of larvapods is, however, general thruout the 

 family. 



In the first instars of Calocala illia, amalrix, inmibens, cara, and of 

 Homoptera hinata the first two pairs are no more reduced than in the other 

 subfamilies mentioned, altho the fully grown larvae of the Catocalinae are 

 typically characterized by the very small size of the first two pairs of 

 larvapods compared to the others. The tendency toward their marked 

 reduction in this subfamily evidently applies to all stadia, rather than to 

 the early ones alone, altho this process has advanced somewhat further in 

 the young larvae than in the old ones, as it generally has throughout the 

 family. The lack of striking difference between the relative size of the first 

 two pairs of larvapods of the early instars and those of the later ones is a 

 fundamental developmental character, which is evidently correlated with 

 the active mode of life of the fully grown larvae of this subfamily. 



