28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



Whether the antennae are segmental appendages serially homolo- 

 gous with the mouthparts and the thoracic legs is a question bound 

 up with that of the segmentation of the head (q. v.). When an 

 antenna is amputated, the flagellum may be regenerated in a form 

 resembling the distal part of a leg, but the significance of this phe- 

 nomenon is uncertain. 



Neck: The neck of the insect is a cylindrical membranous con- 

 nection between the head and the prothorax. It varies somewhat 

 in length in different insects. There are usually various plates, called 

 cervical sclerites, in its walls; a lateral pair of these may form a 

 support for the head by articulating on the postoccipital margin of 

 the latter. The flexible neck allows for movement of the head in 

 various directions by muscles arising in the prothorax and inserting 

 on the postocciput or the postoccipital ridge. 



The morphology of the neck is difficult to understand from its 

 musculature. The principal longitudinal muscles are dorsal muscles 

 from the intersegmental phragma between the pronotum and the 

 mesonotum and extending to the postoccipital ridge of the head, 

 and ventral muscles from the prosternal apodemes to the cross bar 

 of the tentorium. The extent of the muscles, therefore, might suggest 

 that the neck is a part of the prothorax. In this case the postoccipital 

 ridge of the head would be the intersegmental line between the labial 

 segment and the prothorax, but this ridge is evidently the line be- 

 tween the maxillary and labial segments. Otherwise we have to 

 assume that the muscles are those of two primary segments, the 

 labial and the prothoracic, that have become continuous with the 

 obliteration of the intersegmental fold between labial and prothoracic 

 segments. The embryo gives no clue to this problem because the 

 labial segment before it is added to the head is followed directly by 

 the prothoracic segment. Unfortunately, the development of the 

 neck musculature has not yet been followed in the embryo. A larva 

 has no appreciable neck. 



The number of head-neck nuisclcs is variable in different insects. 

 In the locust head, muscles arise from the pronotum as well as from 

 the following phragma. When lateral neck plates are present they 

 usually support the head on anterior processes, but when neck plates 

 are absent the head may be supported on anterior processes of the 

 prothoracic epineura. When a pair of lateral neck sclerites on each 

 side are angularly articulated end to end, attached muscles, by re- 

 ducing the angle, serve to protract the head. The variable structure 

 of the neck contrasts with the standardized structure of a thoracic 



