390 SYNOPTIC COLLECTION. 



observations of Folsom, 1 however, the head of insects is 

 composed of seven segments, each of which, excepting 

 the first (which carries the eyes), bears a pair of append- 

 ages. This naturalist discusses the morphology of the 

 biting mouth parts of insects and their nearest allies, the 

 Crustacea, Arachnida, and Myriapoda, upon anatomical 

 and embryological evidence derived from the most primi- 

 tive insects. The student in search of the natural relation- 

 ships of animals reads with satisfaction the following : " It 

 seems almost superfluous to insist that highly specialized 

 organs can be but imperfectly understood unless studied 

 in egg and larva as well as imago ; that generalized 

 types illuminate specialized forms; and that equivalent 

 groups are linked together through their more general- 

 ized members ; yet too often these accepted principles 

 are not applied." 2 Folsom finds in Anurida maritima 

 Guer., an insect belonging to the Collembola of the primi- 

 tive order Thysanura, seven cephalic segments. The 

 first or ocular segment carries the compound eyes which 

 this investigator homologizes with the compound eyes 

 of Crustacea. The second segment bears the antennae 

 (PI. 947, fig. i, at\ ventral aspect of a portion of the 

 germ band at stage i, x 480) homologous with the anten- 

 nules or first pair of antennae of Crustacea ; the third seg- 

 ment a pair of premandibular appendages (fig. i,pr' l md) 

 homologous with the second pair of antennae of Crustacea. 

 These mouth parts are rudimentary and are not even seen 

 when the specimen is magnified 150 times (fig. 2). The 

 fourth segment bears the mandibles (fig. i, md) homolo- 

 gous with the same organs in Crustacea; the fifth a pair 

 of superlinguae (fig. 3, j/, ventral aspect of cephalic 

 region of germ band at stage 3, x 480) homologous with 

 the first pair of maxillae in Crustacea ; and the sixth and 

 seventh segments bear the two pairs of maxillae homol- 



1 Bull. Mus. Comp. Zool., XXXVI, no. 5, 1900. 



2 Folsom, loc. cit., p. 87. 



