514 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



entomology. On the other hand, its advocates may, of course, point 

 out that adult insects are so specialized that even the embryo in 

 many respects does not repeat phylogeny. Yet it has never been 

 shown that the head is a case in point. It certainly at an early em- 

 bryonic stage consists of a series of segments and no evidence has been 

 offered to prove that these embryonic segments are not true metameres. 



The principal anatomists who have ma])ped out the head on 

 jDurely anatomical grounds are Newport (1889), Janet (1899, 1900), 

 and Verhoeff (1905). Newport went at the subject in the simplest 

 manner possible. He virtually drew circles around the head corre- 

 sjoonding with the plates of the dorsal surface, namely, (1) the lab- 

 rum, (2) the clypeus, (3) the front (clypeus posterior), (4) the small 

 sclerites sometimes found about the bases of the antennae, and (5) 

 the epicranium. He thus had five segments which Avere composed 

 laterally and ventralh^ by whatever fell between two of the inclosing 

 lines. 



Later anatomists have not been satisfied with this direct and simple 

 arrangement by Newport. Janet (1899, 1900) makes out nine head 

 segments which he arranges in three sets of three each and then points 

 out the nice conformity in which the set of three thoracic segments 

 follows. He does not even intimate, however, by what jiatural law 

 tlie head should be a nuiltiple of the thorax, or why his theory should 

 be more plausible by making it such. 



Verhoeff (1905) discredits eml)ryology as a guide in the study of 

 the morphology of the insect head, and, on purely anatomical grounds, 

 elaborates a scheme of eight segments for tlie head of the Dernuiptera. 

 The labrum, the clypeus, and the front, according to his plan, are the 

 first three terga, Avhile the sterna of these segments form the epi- 

 pharj'ngeal membrane and the anterior part of the throat. These 

 segments constitute the " protocephalon." Following them are an 

 antennal segment (a preantennal segment being absent in Der- 

 maptera), and a premandibular segment, constituting the " deuto- 

 cephalon." Finally, the three jaw segments form the "" tritocephalon." 

 The mentum and submentum form the sterna of the labial and max- 

 illary segments, respectivel}^ This vicAv assumes that the maxillae 

 originate behind the labial palpi. In the Chilopoda the so-called 

 maxillae are much more like the ligula and labial palpi of insects than 

 like the insect maxilhr, while the chilopod labium consists principally 

 of the leg-like palpi, thus suggesting that the hexapod first maxilla3 

 are the chilopod second maxilhe. If this should be true, then the 

 theory advanced by Banks (1893) that the poison fangs have co- 

 alesced with the second maxilla) in Chilopoda to form the first max- 

 illae of Hexapoda appears more possible. Otherwise, Banks had to 

 assume that the poison claws moved forward past the bases of the 

 second maxilla? and then fused with the first maxilla\ A combina- 



