Vol. XXV'iii] ENTOMOLOGICAL NEWS. 4O/ 



Another feature which is quite similar in the Phasmids and 

 Grylloblattids, but which is not sufficiently constant in outline 

 to furnish a character of phylogenetic value, is the mandibulare 

 Bm (Figs. 9 and 8), or mandible-bearing sclerite. Comstock, 

 1903, homologizes this sclerite with the trochantin of the leg 

 of the thoracic segments, but it is more than doubtful that such 

 a greatly reduced structure as the trochantin usually is, would 

 be preserved in the mandibular segment. I would be much 

 more inclined to regard this sclerite as representing the coxa 

 of the mandibular appendage, but such speculation is not very 

 profitable until one has carefully compared the mandibles of 

 the Apterygota, Chilopods, Isopods, and lower Crustacea, in 

 which the mandibles become successively more and more leg- 

 like a comparison which I have not yet had time to carry out. 

 Furthermore, I am not yet prepared to say that the basal 

 segment of the mandible of Lepisma (i. e. the portion of the 

 mandible between the terminal portion Md and the trophi- 

 bearing sclerite Tf, in Fig", i) is .the homolog of the mandi- 

 bulare Bm of the Plecopteron nymph (Fig. 4), since several 

 possibilities suggest themselves (e. g. the region immediately 

 above the mandible in Fig. i may represent Bm) in compar- 

 ing the head regions near the mandibles, in the two insects. 

 In order to determine this point, it will be necessary to study 

 a series of Plecopteron and Ephemerid nymphs, examining 

 the musculature in each case, since the musculature furnishes 

 many valuable clues in an attempt to homologize the various 

 parts of a metamere or appendage. 



A study of an extremely interesting series of heads, includ- 

 ing the principal Apterygotan types, the Chilopods, Symphyla, 

 Isopods, etc., has convinced me that the Isopods, Apterygota 

 and "Myriopoda" (sensu lato) are very closely related and 

 were derived from similar forebears. Since the Isopods 

 were probably descended from ancestors resembling the sessile- 

 eyed Arthrostraca (such as Koonunya, etc.), I would consider 

 these Arthrostraca as very near to the common ancestors 

 of Isopods, Insects, and "Myriopods." The Arthrostraca, 

 in turn, were derived from ancestors similar to the Copepods 



