NO. 3 INSECT HEAD SNODGRASS ()3 



bearing the palpus and the galea (as claimed by Borner) ; the muscles 

 of the palpus and the galea pass through the palpifer, but never arise 

 within it. 



i6. The primitive appendage was implanted in the soft lateral wall 

 of its segment, and turned forward and backward on a vertical axis 

 through its base, as does an annelid parapodium. The first joint set 

 off the telopodite, and gave the latter a mobility in a vertical ])lane. 



17. The primitive muscles inserted on the base of a generalized limb, 

 as on an annelid parapodium, consisted of a dorsal promotor and a re- 

 motor, and of a ventral promotor and a remoter. When tergal plates 

 were developed, the gnathal appendages of the arthropods became 

 attached to their lateral margins, each by single point of articulation. 

 The ventral muscles of the appendages then became sternal adductors. 



18. The points of origin of the ventral adductors of the gnathal 

 appendages in myriapods and insects were probably crowded together 

 when the gnathal segments were added to the protocephalon. They 

 have since become supported on a pair of apophyses arising at first 

 from the base of the hypopharynx. In the myriapods and in most of 

 the apterygote insects, the apophyses still maintain their hypopharyn- 

 geal connections : but in the pterygote insects their l)ases have migrated 

 laterally to the margins of the cranium, and in all but some of the 

 lower forms have finally moved to a facial position in the epistomal 

 suture. Their posterior ends have united with the transverse ten- 

 torial bar developed in the back part of the head. The hypopharyngeal 

 apophyses of the Myriapoda and Apterygota have thus come to be 

 the anterior arms of the pterygote tentorium. 



19. The adductor muscles of the insect maxillae, arising on the 

 tentorium, are the sternal adductors of the appendages, corresponding 

 with the sternal adductors or rotators of the thoracic legs, and are 

 derived from the primitive ventral promoters and remotors of the 

 limb. 



20. The ventral adductors of the mandibles in the Chilopoda re- 

 tain their connections with the sternal, or hypopharyngeal, apophyses. 

 In the Diplopoda, Crustacea, and Apterygota, groups of the adductor 

 lil)ers from the mandibles have lost their sternal connections and have 

 united with each other by a median ligament to form a dumb-bell 

 muscle between the two jaws. Other groups of fibers may retain their 

 connections with the apophyses, or direct with the base of the hypo- 

 I)harynx. In the Pterygota, the ventral adductors of the mandibles have 

 been lost, except for a few rudiments in some of the lower orders. 



21. The mandible of Lcpisma and of pterygote insects is hinged 

 to the head on a long base line with anterior and posterior articulations. 



