AND OTHER INJURIOUS INSECTS OI' \i)0/ ANT) I(jo8. 189 



base, which become more marked distally, and grade into a hexagonal 

 figure near the end. In some of the higher genera there is a deep 

 furrow encirchng th.e cornicle near its distal end. 



The Cauda: The cauda is an extension or appendage of the 

 last abdominal segment. In Lachinis, which shows more primitive 

 characters than any other genus of the Aphidid(c, the ninth segment is 

 rounded at the end and there is no distinct cauda present. In those 

 genera where a distinct cauda is present four predominant types may be 

 recognized The conical form found in Aphis and in the larva and pupa 

 of the higher forms is about two or three times as long as it is broad 

 and is directed slightly upward. The ensiform type of the higher 

 genera, which was probably derived from the conical form, is very long 

 and slender, curved upward, and sometimes enlarged in the middle. 

 The globular form which may also have been derived from the conical 

 type, has its end swollen on the ventral side into a large globular ap- 

 pendage. The obsolete cauda found in the gall-makers is the result of 

 degeneration probably from a conical type. The cauda is in this case 

 a very short rounded extension of the ninth segment. 



The hairs on the cauda very often have a definite arrangement 

 and afford good specific characters. In the ensiform cauda there is a 

 terminal curved hair and a row of stout hairs on each side. Each 

 hair corresponds to one on the opposite side, so that there may be 

 from two to fourteen pairs. On the dorsal side of the globular type 

 there is often a prominent spine which is not armed with hairs. The 

 cuticle of the under side of the cauda is covered with a thick mass of 

 short sharp points. The dorsal side is imbricated. In Aphis there is 

 a transparent surface on the dorsal side of the cauda near its base. 

 This may be a provision for a movement of the cauda. 



The Anal Plate: The anal plate is situated on the ninth ab- 

 dominal segment just ventral to the cauda. In its typical form it is 

 nearly hemispherical, but in the larva and pui)a it is not much more 

 than a flattened plate on the ventral side of the abdomen anterior to 

 the anus. In CaUiptcnis and related genera the anal plate is emarginate 

 when seen from the dorsal side. There are some species where it is 

 only divided by a shallow notch, while in others this notch is deepened 

 so that the anal plate is divided into two parts, one on each side, with 

 the cauda, which is not much longer than they are, attached almost be- 

 tween them. The anal plate is always thickly covered with hairs. On 

 its ventral border there is a row of three protuberances called genital 

 armature bv Buckton, each of which bear several short slender hairs, 



