3111 NOCTUID LARVAE— RIPLEY 69 



The race-history of the reduced epicranial stem may be represented by 

 the diagram shown in figure 61, which indicates both the independent origin 

 and progressive nature of this condition. In this figure 1 represents the 

 persistence of the long-stemmed ancestral condition to the present. A 

 form which has departed relatively recently from the condition of 1 and 

 which tends toward the development of a shorter stem is illustrated by 2. 

 The most ancient departure from 1 is represented by 6, which reveals the 

 shortest epicranial stem at present. The conspicuousness and apparently 

 fundamental nature of this character would tempt taxonomists to employ 

 it for the division of larger groups within this family. Our knowledge of its 

 phylogeny, however, derived from this postembryological study limits its 

 taxonomic use to the separating of species and in some cases, perhaps, of 

 genera. The taxonomist studying this structure without regard to postem- 

 bryological evidence, but drawing his conclusions entirely from the com- 

 parative morphology of the last instar, would, in all probability, be misled 

 as to its phylogeny. He would, of course, without the aid of postem- 

 bryology correctly conclude that the short stem represented a specialized 

 condition but, on the other hand, no clue as to the independent origin of the 

 shortening of this suture would be afforded him. Working on this basis' 

 he would most naturally be led to beUeve that the species with the shor^ 

 epicranial stem represented, at least for the most part, a phylogenetic unit- 

 The fact that this condition is often found in closely related genera would 

 add to this impression. Its independent origin in different species in the 

 same subfamily or genus could not possibly be deduced without a post- 

 embryological study. Figure 60 represents diagrammatically the erron- 

 eous interpretation of the evolution of the short epicranial stem, which 

 would be most naturally derived from a study confined to full-grown larvae. 

 In this diagram 1 represents the persistence of the primitive long-stemmed 

 condition, as in Figure 61. The short-stemmed condition, on the other 

 hand, is shown as descending from a common ancestor. The preservation 

 of the condition of the most ancient departure from 1 is illustrated by 2, 

 whereas in reality the condition of 2 is the most recent departure in this 

 direction. According to Figure 60, 6 has developed most recently and 

 reveals the most extreme speciaHzation. In reality the condition of 6 at the 

 present time is found in species in which this tendency appeared earliest in 

 phylogeny, as shown by Figure 61. A comparison of these two diagrams, 

 the correct and the false, derived respectively with and without regard to 

 postembryology, demonstrates in a convincing manner the phylogenetic 

 value of this neglected source of e\'idence. 



POSTEMBRYOLOGY OF LABIUM AND SPINNERET 



The most profound postembryonic changes undergone by noctuid 

 larvae are those in the form of the spinneret, while other parts of the labium 



