39] LEPIDOPTEROUS LARVAE — FRACKER 39 



insect larva having the setal plan of all the segments similar and 

 including only the primary setae as given above. 



The ancestral type has been modified in three ways, each being 

 more or less independent of the other two. (a) The prothorax shows 

 a tendency to retain the maximum number of setae ; this is a response to 

 the numerous sensory stimuli which this segment must transmit, (h) The 

 mesothorax and metathorax show a partial reduction and considerable 

 modification in response to the necessary mobility of this portion of the 

 body, (c) The abdominal chaetotaxy has also been reduced but the 

 setae tend to retain their original typical position. Segments 9 and 10 

 show specialized modifications of the setal arrangement of segments 

 1 to 8. 



Subprimary setae are those which, altho they have a definite location 

 on the mature larva and are rather persistent, are absent from the 

 first instar. 



New setae have usually appeared first in that part of the body in 

 which they were of most benefit, e. g., gamma on the prothorax and eta 

 on the abdomen. In some cases setae which seem to be homologous with 

 them have arisen later on other segments. The order of their appearance 

 is now shown in ontogeny. 



In addition to the doubtful subprimary homotypes of gamma 

 and eta, there are two rather persistent subprimary setae : theta, which 

 is found on the mesothorax and metathorax of both suborders and on 

 the abdomen of Jugatae; and mu, which is more recent and appears 

 only on the abdomen of Frenatae. 



Subprimaries of less common occurrence are omega and phi of the 

 Tau group, while still others are present in certain families. 



Primary or primary and subprimary setae tend to associate with 

 each other in groups. These groups are indicated in this paper by 

 capital letters. 



The Beta group consists of alpha and beta; Rho, of epsilon and 

 rho; Kappa, of theta, kappa, and eta; Pi, of pi and nu; and Tau, of 

 tau, omega, and phi. On the abdomen tau is associated with the Pi group. 



Both primary and subprimary setae may develop into tufts borne on 

 verrucae. The verrucae of the same setal group tend to coalesce, while 

 those of different groups tend to remain distinct. 



SYNONYMS 

 In the following tables are given the names used by various authors 

 for the different setae on the segments heretofore studied. A parenthesis 

 indicates that the seta is subprimary in the region of the body referred 

 to. "0" indicates that the seta is absent from that region; while a 

 dash is used when the author fails to mention the seta. 



