March 18, 1808,] 



SCIENCR 



375 



This paper by Dr. Heyinons, based on 

 embryological data, is, however, very im- 

 portant when carefully studied, though in 

 some respects the assumption that the beak 

 is the labium has led, in my opinion, to 

 false conclusions. After disposing of Kra3- 

 pelin's contention that the inner and partly 

 united pair of lancets represent the man- 

 dibles, he states, as his first proposition, 

 that the lateral lancets are produced from 

 the mandibles, which are peg-like, and are 

 withdrawn into the head. This is modified 

 in the seventh proposition, in which it is 

 stated that the so-called mandibles are 

 really only the lobes of the mandibles, of 

 which the stem has become rudimentary. 

 Yet, further, it is limited in the eighth prop- 

 osition that in the Heteroptera, finally, the 

 mandibular stem is entirely lost and united 

 to the anterior part of the juga; but as this 

 leaves an unattached lancet floating about, 

 we find in the fourth proposition that in 

 the Heteroptera the maxillary stem 'is 

 usually divided into two parts. On one, 

 which I call lamina maxillaris, occui'S the 

 musculus protractor of the lateral lancets 

 (mandibles). Difierently stated, this means 

 that a peg-like process is identified as a 

 mandibular lobe whose stem disappears, 

 which is retracted into the head, where 

 it forms a lancet whose musculus pro- 

 tractor is attached to the stem of the 

 maxilla ! Now a lobed mandible is a rarity 

 in insects, and where a lobe does occur it is 

 either an insignificant appendage or is 

 firmly united to the base. An absence of 

 the lobe is the rule, everywhere; in no 

 mandibulate is the lobe ever the only part 

 represented. Here we are supposed to see 

 the stem disappear and the lobe developed 

 into an appendage attached to the maxillary 

 stem. 



If the musculus protractor is attached to 

 part of the maxillary stem, which I have 

 no doubt is the case, why not consider the 

 lancet maxillary, and as lacinia, or inner 



lobe? This would make its attachment 

 and association perfectly normal. Does it 

 not seem just a little absurd to claim that 

 such organs as the mandibles can become 

 practically maxillary appendages ? 



The second proposition is that the median 

 (inner) lancets are not made up by the 

 maxillfe in toto, but only by their lobes, 

 which are also peg- like and retracted into 

 the head. The third proposition is in part 

 that the trunk of the maxilla after the re- 

 traction of the lobes agrees in essentials 

 with the palpi maxillaris of other insects. 

 That is exactly what it ought to do if the 

 lancet is the produced palpifer which I be- 

 lieve it to be. 



Dr. Heymons proves, therefore, to my 

 mind, that one pair of lancets is palpifer 

 from the maxillary palpi, the other lacina 

 from the stem of the maxilla ; and this is 

 exactly the conclusion which I reached from 

 comparative studies. The muscles from 

 both lancets are supplied from maxillary 

 structures exclusively. 



The fifth proposition is that ' rudimentary 

 maxillary palpi are recognizable at the 

 roots of the beak'. In ISTepa, for instance, 

 they are approximately onion-shaped and 

 placed before the juga. This it seems to 

 me indicates that the beak is also maxil- 

 lary, but the ninth proposition is that the 

 beak is derived from the third (hinder) 

 embryonic pair of jaws. The development 

 teaches that in the Ehyngota this pair re- 

 mains simple. On the labium neither palpi 

 nor lobes, nor any structure that may be 

 considered such, occur. Labial palpi, con- 

 sequently, are lacking in all Rhyngota. 



If these embryonic processes forming the 

 beak are really those of the labium, would 

 not the entire absence of lobes or append- 

 ages be an unusual character ? Assuming 

 them to be, as I believe, the maxillary galea 

 all difiiculty vanishes. 



The truth is. Dr. Heymons started with 

 the conviction that he must find three em- 



