j^o. 5. — The Development of the Mouth-Parts of Anurida 

 maritima Guer?- By Justus Watson Folsom. 



CONTENTS. 



Introduction 87 



Methods 88 



General Description of Egg ... 89 



Reference Stages 90 



Procephalic Lobes ...... 91 



Labrum and Clypeus 93 



Antennae 96 



Preraandibular Appendages ... 98 



Mandibles 102 



Lingua and Superlinguae .... 110 



Maxillae 119 



Labium 126 



Skull 135 



Tentorium 139 



Segmentation of the Head . . . 142 



Summary 146 



Bibliography 151 



Explanation of Plates 157 



Introduction. 



Our present ideas of homology in the details of insect mouth-parts 

 rest almost exclusively upon anatomical data, and need careful revision 

 in the light of embryological facts. 



Too many entomologists have speculated upon the subject in complete 

 disregard of evidence from ontogeny or phylogeny. Embryologists, on 

 the other hand, have greatly neglected the mouth-parts. 



It seem.s 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. 



The objects of the present paper are two : first, to supplement my pre- 

 vious account (Folsom, '99) of the anatomy and functions of the mouth- 

 parts of a representative Collembolan ; second, to discuss the morphology 

 of raandibulate mouth-parts of insects and their nearest allies upon 

 anatomical and embryological evidence derived from the most primitive 

 insects, the Apterygota. 



1 Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology at Harvard College, E. L. Mark, Director, No. 114. 

 VOL. XXXVI. — No. 5 



