161 



THE MAXILLARY TENTACLES OF PRONUBA.* 



By John B. Smith, Sc. D., Neiv Brunswick, JSf. J. 



In Ms excellent studies on the genus Pronubii Dr. C. V. Riley has 

 called si)ecial attention to the peculiarities of the mouth structure, 

 and ^particularly to the develojiment of a so-called '^ maxillary tentacle." 

 The figures given of this structure in the various species are so ex- 

 cellent that they at once aroused a suspicion in my mind that, while 

 they were really special develoi)ments in one sense of the term, so far 

 as we now know unique in Lepidoptera, yet that there were similar or 

 homologous structures elsewhere, in other orders; that is to say, 

 there is really no new organ or process, only a mere adaptation or 

 development of a known maxillary sclerite, which is paralleled by 

 more or less similar developments or adaptations of the same sclerite 

 in other groups. To the courtesy of Dr. Eiley I owe a sui)ply of alco- 

 holic sjyecimens of Fronuha yiiGcasella for examination, and from a care- 

 ful study of these I have concluded that the so-called '^ tentacle " is really 

 an extension of the palpifer or palpus bearer. Of all the Lepidoptera 

 known to me, Pronuba has the maxillary sclerites best developed. Dr. 

 Riley has called attention to the fact that the two halves of the spiral 

 tongue are not united, as is usual in the higher Lepidoptera, to form a 

 a tube, and I find that when the two maxillae are dissected ofi' the 

 structure bears a remarkable resemblance to that found in the Cole- 

 opterous genus J^emognatha, and while the lacinia is wanting, some of 

 the other sclerites are even better marked. A comparison of the figures 

 of Nemognatha and Pronuba male will at once emphasize this simi- 

 larity. 



In the male Pronuba the ''maxillary tentacle" is not developed; but 

 if we examine the large sclerite at the base of the palpus, which is a i)al- 

 pifer without doubt, we see, evidently, the structure whose specializa- 

 tion forms the ''tentacle." This special development of the palpifer is 

 not unique in Pronuba, but is of common occurrence in the piercing 

 Diptera, Erax offering an excellent example. In a paper published by 

 me in the Trans. Am. Ent. Soc, xvii, 1890, I showed the modifications 

 of this structure in the Diptera; but. I was unable at that time to de- 

 cide whether I had to do with a palpifer or with a stipes, because spe- 

 cialization and division of parts was carried to such an extent that the 

 connection between the original sclerites was obscured. In the Hem- 

 iptera as well, the same sclerite is developed into a piercing organ, 

 although the maxillary palpi themselves are rudimentary. 



It maybe objected that these structures of the Diptera and Hemii:>tera 

 are rigid, chitinous x)rocesses, without tactile functions, while in Pro- 

 nuba the process is flexible and set with numerous tactile or specialized 

 spinules. This kind of change, however, is not unusual in insects, and 

 precisely the same difference appears between the rigid chitinous ligula 



*Read before Section F of the A. A. A. S., at the Rochester meeting, August 18, 

 1892. 



