NO. 6 INSECT ABDOMEN — SNODGRASS 97 



crochets, are retained in the pupa, and Bottinier (1926, fig. 3 A) 

 shows a similar retention of the anal legs in the pupa of Chaetocampa 

 crotonella. It is unfortvniate that socii are absent in these species, 

 for we might expect to find the socii developed within the anal pro- 

 legs of the pupae. More positive evidence of the identity of the termi- 

 nal larval appendages with the terminal appendages of the adult is pre- 

 sented by Middleton (1921) in a study of the chalastogastrous Hy- 

 menoptera. Middleton claims that the anal prolegs, or postpedes, of the 

 larva of Ptcronidea rihesn are transformed during metamorphosis into 

 anal lobes of the pupa, and that within these lobes are developed the 

 so-called " cerci " of the adult sawfly. These appendages of the adult 

 insect, he points out, are not borne by the tergum of the anal segment, 

 but arise from a lateral membranous area of the venter of this seg- 

 ment, and thus morphologically have the same position as have the 

 postpedes of the larva. The anal segment in both the larval and the 

 adult sawfly is numerically the tenth abdominal segment, and its ap- 

 pendages are therefore not the true cerci in either case. 



Trichoptera. — The abdomen of trichopterous larvae lacks appen- 

 dages except on the terminal segment. In some forms, as in Platyphy- 

 lax designatns, a fringe of slender setae along each side of the abdomen 

 from the second to the end of the eighth segment (fig. 41 A, B, a) 

 evidently marks the dorso-pleural line separating the dorsum of the 

 abdomen from the region of the limb bases {LB), since, if the line of 

 this fringe were carried into the thorax, it would run dorsad of the 

 thoracic subcoxae (A, Scxz). On the ninth segment there is nothing 

 to mark the dorso-pleural boundary ; but on the terminal segment 

 the base of the appendage (B, P/^) has a lateral position corresponding 

 with the limb base areas of the segments preceding the ninth. The 

 terminal segment of Platyphylax is a hemispherical lobe with a long, 

 median anal cleft on the ventral part of its distal surface {An). It is 

 evidently the tenth somite, or pygidial segment. 



The pygopods of trichopterous larvae differ considerably in different 

 families and genera. Their principal variations have been described by 

 Ulmer (1903) and by Krafka (1924). According to Ulmer there 

 are two principal types of these appendages. Those of one type are 

 short ; those of the other, characteristic of Hydropsychidae and Rhya- 

 cophilinae, are long and leg-like. In both types the limb terminates in 

 a hook-like claw. The structure of the two forms of appendages 

 is here illustrated from Platyphylax designatus (fig. 41 B, Pp) and 

 an unidentified species of Hydropsyche (F, Pp). 



In Platyphylax designatus each larval pygopod together with its 

 supporting structure (fig. 41 B, Pp) consists of a large basal plate (C, 



