June, i9i6.] FORBES : CATERPILLAR HOMOLOGIES. 137 



ON CERTAIN CATERPILLAR HOMOLOGIES. 



By Wm. T. M. Forbes, 

 Ithaca, N. Y. 



A recent paper by Stanley B. Fracker^ raises some interesting 

 questions as to the interpretation of the caterpillar setae. He takes 

 the prothorax as a typical segment, having the largest number of 

 sets of any simple segment, names its setae, and then, assuming the 

 setae of the following segments are strictly homologous, so far as 

 they go, applies to them the same names. My belief is that the cor- 

 respondence is partial, and so far as the prothorax is concerned con- 

 fined to a couple of the mid-ventral, and possibly the mid-dorsal setae. 

 In the following discussion the thoracic setae will be referred to by 

 the Greek letters applied to them by Fracker, the abdominals, by the 

 numerical system now in use, derived, so far as the principal setae 

 are concerned, from Wilhelm Miiller. 



The abdominal set^e consist of i, ii, iii and iii a. which lie above 

 the spiracle, iv and v, between the spiracle and the subventral fold; 

 vi between this fold and fold psi, appearing only after the first moult, 

 vii on the outer side of the leg-base, typically of three setae, and 

 viii on the inner side, near the mid-ventral line ; besides these ix, sub- 

 ventrally, and x subdorsally are minute setae, lying close to the in- 

 cisure and touching the posterior curve of the preceding segment ; 

 presumably, like our own tendon-organs, they serve to report to the 

 caterpillar its own position. 



In the Hepialidae there is a slight modification, the three serae 

 nearest the spiracle, behind and below, are in an oblique row, and 

 placed high up;^ I have assumed that these are iv, v and vi, moved 

 up and back, as they have in Incurvaria."* Fracker assumes that the 

 two lower are iv and v (kappa and eta), that the upper is a new sub- 

 primary (theta), and that the usual subprimary vi (mu) is absent. 

 In the first stage, as figured by Dyar, there are only two setae very 

 slightly higher than the two lower of the row in the last stage. The 



1 The Classification of Lepidopterous Larvae ; Illinois Biological Mono- 

 graphs : II, I ; 1915, Urbana, 111. 



2 Ann. Ent. Soc. Am., Ill, pi. 12, fig. 33. 



3 L. c, fig. 34. 



