516 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxti. 



MachiJis are homologous with the first maxillaD of Crustacea, and 

 Folsom concurs in this view. Apparently no one has compared them 

 with the paragnatha of Crustacea. 



Holmgren (1907), on the other hand, claims that these superlingual 

 processes arise from the premandibular segment and are innervated 

 from the tritocerebrum. It would seem that he must refer to a 

 different pair of aj^pendages, namel}^, the second antennal rudiments 

 or " intercalarj' appendages."' His observations were made on a fly 

 larva ( Ph alacroecra ) . 



Bengtsson (1897, 1905), however, describes an endolabium in 

 Phalacrocera which includes '' paraglossa\'"' equivalent to the super- 

 lingUcP of lower insects. Holmgren (1907) refutes this idea entirely, 

 and claims that Bengtsson's so-called endolabium of fly larvae is not 

 the endolabium of lower insects but simply the terminal lobes of the 

 ordinary outer labium, of which Bengtsson's '" ectolabium " is the 

 mentum and submentum. He furthermore asserts that what Beng- 

 tsson takes for nerves going to this endolabium from the superlingual 

 ganglion are simply muscle fibers, though Bengtsson (1905) had 

 stoutly defended his former observations (1897). 



The best summarized statement of the segmentation of the head 

 is that made by Comstock and Koclii (1902). Although some work 

 has been done since, but little new information has been added. The 

 preoral part of the head consists of three embryonic segments cor- 

 responding with the three lobes of the brain, namely, the protocere- 

 brum. the deutocerebrum and the tritocerebrum. The first segment 

 has no appendages, but it innervates the eyes; the second is the 

 antennal segment ; the third carries the '' intercalary appendages "■ — 

 vestigial organs observed by many embryologists in the Aptera 

 (AAlieeler 1893, Uzel 1897, Claypole 1898. Folscm 1900), possibly in 

 the Diptera (Holmgren 1907), and in the Ilymenoptera (Biitschli 

 1870). These rudimentary appendages correspond with the second 

 antennir of Crustacea. 



The postoral region of the head and the mouth parts are certainly 

 derived from at least three embrj'onic segments, or, according to 

 many embryologists, from four. The first is the mandibular segment. 

 The possible second is the one under dis])ute, but so many eml)rvolo- 

 gists have described two small appendages back of the mandibles 

 which fuse with the median lingua to form the hypopharynx that 

 their existence can not be doubted, and it is reasonable to suppose 

 they represent a segment. Riley (1904), however, shows tliat these 

 superlingual appendages, or maxilhihv, are absent in the embryo of 

 Blafta, and he doubts that they are actual appendages where ob- 

 served. Berlese (190G) also does not recognize a superlingual seg- 

 ment. Following this doubtful metamere is the segment of the first 

 maxilla^, and finallv that of the second nuixillne or labium. 



