THE INSECT HEAD SNODGRASS 



455 



said to be developed in the embryos of more primitive insects sepa- 

 rate from the lingua and somewhat anterior to it. They are, there- 

 fore, regarded by some writers (Folsom, 1900, Denis, 1928, Hansen, 

 1930) as a pair of true segmental appendages in the gnathal region 

 of the head. In the apterygote family Machilidae the superlinguae 

 have a structure suggestive of their being reduced appendicular 

 organs (fig. 7 B), each having two terminal lobes (a, h), and near its 

 base a small, palpuslike process (c). 



A hypopharyngeal structure similar to that of the apterygote 

 insects occurs in some of the Crustacea (fig. 7 C), but the lateral 

 lobes of the crustacean hypopharynx are called paragnatha (Pgn), 

 and the median, lingual lobe is not always present (fig. 18 B). 

 Because of the similarity between the superlinguae and the para- 

 gnatha many students of arthropods, following Crampton (1921), 



c 



Figure 7. — Showing similarity in structure of the hypopharynx between certain 

 insects and some crustaceans 



A, hypopharynx of an apterygote insect, Nesomachilis, composed of a median 

 lingua (lAn) and lateral superlinguae (Slin), posterior view. B, left super- 

 lingua of same, anterior view. C, Hypopharynx of an isopod crustacean, 

 formed of median lingua and lateral paragnatha (Pgn), posterior view. 



have regarded the two organs as homologous structures. Others, 

 however, including Folsom (1900), Henriksen (1929), Hansen 

 (1930), and Tuxen (1931), believe that the superlinguae are the 

 first maxillae (maxillulae) of Crustacea, and that the paragnatha 

 are not appendicular organs. Folsom (1900) claimed to have 

 found in a collembolan insect that the superlinguae are innervated 

 from a special center in the suboesophageal ganglion of the head, 

 as does also Denis (1928), but the two investigators do not agree 

 as to the position of the nerve center. On the other hand, Philip- 

 tschenko (1912) denies the existence of a superlingual nerve center, 

 and Hoffman (1911) asserts that the superlinguae are mere second- 

 ary outgrowths of the head wall at the inner angles of the mandibles. 

 The idea that the paragnatha of the Crustacea are segmental append- 

 ages appears to have no champion, though Denis (1928) recognizes 



