92 



Riley Some Interrelation* of Plants and Insects. 



portant structures has not proceeded so far in Pronuba i/uccawlla 

 as in P. maculata, which pollinizes Yucca irhtpplei. Those not 

 familiar with the structure of Lepidoptera will hardly appreciate 

 the modifications to which I shall allude, however, without the 

 preliminary statement that the tongue in Lepidoptera consists 

 of two distinct parts (maxilla?) which are more or less concave 

 on their inner side and united at the borders of the concave por- 

 tion by certain locking arrangements to form between them the 

 sucking tube. Now, while inmost cases the two parts may be 

 relaxed and separated by force, in nature they are never so sepa- 

 rated, while the tip of the tongue is more or less acuminate and 

 the two parts here very firmly united. 



Fin. 7. PKONUBA MACULATA : a, tip of female abdomen; bj o, basal joint of ovipositor: 

 tj o, terminal joint of ovipositor; ov, oviduct; m p, max. palpus; m /, maxillary tenta- 

 cle; t, tongue ; gs, claspers of male from side; #/>, claspers of male from behind en- 

 largemant indicated; pr, front wings, showing arrangement of spots in two of the more 

 common forms, hair-lines showing natural si/e. 



In Pronuba yuccasella I had often noticed that the two part* 

 became separated and in fact were almost always separated 

 toward the tip, thus suggesting a loss of function as a sucking 

 organ, but otherwise the tongue is strongly developed, and, with 

 the exception of the weakness of the locking arrangement, not 

 particularly abnormal. In Protmbamaculata, however (Fig. 7), 

 the two parts of the tongue are but very feebly united, and often 

 more or less disconnected, and are actually thickly covered with 

 minute hairs and more sparsely with longer spinous hairs, inter- 

 mixed ; they are also swollen and enlarged toward the base. The 

 import of this fact can best IMJ conveyed to you by the statement 



