52 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



and if so, they probably lay more eggs on the preferred varieties. 

 No attempt was made in the present investigation to determine which 

 was true, but it is certain that the larvae can distinguish apples by 

 smell and touch, and the moths are certainly guided by tropic stimuli 

 to the proper places for depositing eggs. A study of this kind raises 

 more cjuestions than it answers, yet there is no other way to make 

 progress. Not l)eing able to throw light on this question, a thorough 

 study of the morphology of the sense organs of the codling moth and 

 its larvae was made, hoping that a little light might finally be had. 



Since the moths are nocturnal fliers, their eyes cannot be their 

 chief sensory receptors for locating the proper host plant. As already 

 stated, the eyes of the larvae change slowly from photopositive ones 

 in the first instar to strongly photonegative eyes in the last instar. 

 This change may be caused by a migration of pigment, as found in 

 certain other larvae, and it seems to be in harmony with the habits of 

 these larvae, which spend most of their time inside of fruit. Before 

 entering apples, photopositive eyes are needed ; but after emerging for 

 the purpose of pupating, photonegative eyes are required. 



Two kinds of smelling organs — certain hairs on the antennae, and 

 the pores, called olfactory by the writer — are fully described. It seems 

 doubtful whether these hairs, called pit pegs and end pegs, can serve 

 as olfactory organs owing to their hard covering of chitin. Granting 

 that these hairs are the only olfactory receptors of Lepidoptera, eight 

 of the 34 individuals discussed in table 2 cannot smell at all, while 

 four others can smell only slightly. The codling moth, however, has 

 a good supply of them. Larvae do not have these so-called olfactory 

 organs, yet they can smell. The olfactory pores are common to both 

 adult Lepidoptera and their larvae. In the adult they are found on the 

 wings, legs, mouth parts, and second segment of the antennae. In 

 the larvae they occur on the head, mouth parts, antennae, legs, first 

 thoracic segment, and anal prolegs. 



There are supposedly two types of taste organs. The first type 

 consists of certain hairs on the mouth parts, but since these are covered 

 with hard chitin the writer does not believe that aqueous liquids can 

 pass quickly through them in order to stimulate the nerves inside. The 

 second type is Minnich's tarsal chemoreceptors, which, when properly 

 stimulated, are 256 times as sensitive as are the taste organs in the 

 human mouth. We know nothing about the structure of these recep- 

 tors, and the present writer so far has found only two kinds of sense 

 organs — sense hairs and olfactory pores — in the tarsi of insects. 



