147 



PHYI.OGENY 



The characters used as a basis for determining the phylogeny of 

 the order are primarily: (i) the nmnber of movable segments; (2) 

 the freedom of the appendages; (3) the number of sutures present 

 in the head; (4) the relative length of the body segments; (5) the 

 presence or absence of visible labial palpi and maxillary palpi ; (6) the 

 presence of exposed portions of the prothoracic femora in special- 

 ized pupae; and (7) the method of dehiscence. 



In the most generalized forms there is complete freedom of mo- 

 tion possible between the head and thorax, and between all the seg- 

 m.ents of the thorax and abdomen with the exception of the eighth, 

 ninth, and tenth abdominal segments, which are always fixed. As 

 specialization proceeds, there is a gradual loss of motion ; first between 

 the head and thorax, then between the segments of the thorax, and 

 last of all between the different segments of the abdomen. The loss 

 of motion in the abdomen begins first at the cephalic end, but by the 

 time that complete motion of the second segment has been lost there 

 begins a loss of motion of the seventh segment. This takes place first 

 in the female, and there is a large series of forms, including the super- 

 families Gracilarioidea, Tortricoidea, and Aegerioidea, which retain 

 freedom of motion in the seventh segment of the male, while there is 

 taking place at the cephalic end of the abdomen the loss of motion of 

 the third abdominal segment. There are, however, a few gen- 

 era of Gracilarioidea which have lost freedom of motion of all 

 the body segments and which form the most specialized end of 

 that series. The pupae which have lost motion of all the abdominal 

 segments except the fourth, fifth, and sixth, are those usually referred 

 to as obtected pupae. There are few pupae more specialized than 

 those of the superfamily Gracilarioidea which retain freedom of 

 motion of the seventh abdominal segment in the male, but there are 

 a few generalized forms both in the Pyralidoidea and Papilionoidea in 

 vvhich this is the case, as it is also in the family Epermeniidae of the 

 Yponomeutoidea. These three superfamilies are usually considered 

 as more specialized than the Gracilarioidea. As the number of mov- 

 able segments determines the position of a superfamily in the series 

 it is readily seen that these superfamilies must be considered as more 

 generalized than those in which motion is lost in the seventh segment 

 ill the male. It will be remembered that a segment is spoken of as 

 movable when motion is possible between its caudal margin and the 

 segment caudad of it. As the appendages become soldered to the body 

 wall on the ventral surface no motion of this part of the segment is 

 possible if the incision between its caudal margin and the next seg- 



