10 



small basal one, however difficult sucli may be to perceive. And, indeed, 

 the presence of this infinitesimal joint has never, in point of fact, been 

 questioned, though Lacordaire rightly defines it as "a peine distinct." 

 It is the third one on which a diflference of opinion prevails. Man- 

 nerheim, though rightly pronouncing the labial palpi to be triarticulate, 

 nevertheless (as has been pointed out by Kedtenbacher), mistook the 

 fascicle of hairs which terminate the ti'ue apical joint /or the joint itself, 

 and consequently regarded the second and third joints as a single one. 

 Of all the diagnoses to which I have access, M. Duval's is the only one 

 which properly describes this (so-called) "second joint;" for although, 

 in deference to preceding writers, he records the organ (in his diagnosis) 

 as biarticulate, he, nevertheless, adds in a foot-note : "Toutefois quoique 

 les palpes labiaux n'offrent en apparence que deux articles, on doit, je 

 crois, considerer le troisieme comme se trouvant intimeinent sonde au 

 second et se confondant avee lui; car, avec un peu d' attention, j'ai pu 

 voir parfois une legere trace de suture transverse." Had he viewed the 

 palpus in a globule of clear fluid by means of polarized light, he would 

 have had no doubt as to the existence of this "transverse suture" which 

 separates tlie real third joint from the inflated second one (of which it 

 has been supposed hitherto to constitute but the conical, or mammiform, 

 extremity) . 



As regards the ligula, there is also a little discrepancy in the pub- 

 lished diagnoses ; and certainly its exact structure is not very evident. 

 The large and rather narrowed anterior central region of the (hexagonal) 

 mentum is straightly truncated in front, and has, at a slight distance 

 below its anterior edge, a very distinct transverse line, or suture, which 

 gives to the extreme apical portion all the prima facie appearance of 

 being a short corneous ligula, and as such, indeed, it has been actually 

 described, both by Eedtenbacher and Lacordaire; yet I think it is 

 nevertheless evident, as M. Duval has shewn, that it cannot be a part 

 of the true ligula, inasmuch as it is not only in the same place with the 

 mentum, but is clearly articulated on to the front margin of the latter ; 

 whereas, the ligula must necessarily be situated behind the mentum, 

 even though contiguous (and occasionally also soldered) to it: and, 

 indeed, in this particular instance, the position of the palpi (which arise 

 from behind the middle of the mentum) would imply as much, still 

 further. Hence, M. Duval's figure, which represents the ligula as 

 membranous, and just jirojectiug beyond the anterior angles of this 

 articulated front portion of the mentum, is probably correct ; though at 

 the same time I must confess that my microscope has failed (in two 

 dissections, of different species) to bring out satisfactorily that exact 



