IN THE LARV^ OF ANISOPTERID DRAGONFLIES. 



141 



nucleated syncytium, and must be regarded as a highly specialized structure 

 derived from an originally typical proctodseal epithelium with separate cell- 

 boundaries. Except at certain definite places, where it swells up into the 

 thick turgid structures known as the basal pads, this syncytium is a flat 

 pavement-like layer containing numerous nuclei at fairly regular intervals. 

 In some forms it is entirely unpigmented throughout ; in others, especially 

 at certain places, dense masses of pigment-granules are present and hide the 

 nuclei from view. 



mcr 



Text-fig. 1. — Transverse section through seventh abdominal segment of the larva of 

 jEschna brevistyla, Ramb., 4th instar, to show position and structure of gill-basket. 

 ( X 32.) 



cf, cross-fold ; cut, cuticle ; dt, dorsal tracheal trunk ; ect, ectoderm ; /6, fat-body ; 

 gf, main gill-fold ; ht, dorsal vessel or heart ; mcr, circular muscle-layer of gill-basket ; 

 mid, dorsal longitudinal segmental muscle ; mlp, Malpighian tubule ; mlr, longitudinal 

 muscle-band of gill-basket ; mlv, ventral longitudinal segmental muscle ; mt, trans- 

 verse segmental muscle ; vg, ganglion of ventral nerve-cord ; vnt, ventral tracheal 

 trunk; vst, visceral tracheal trunk. 



The protoplasm of this syncytium is only very slightly chromatophil, 

 giving only a light purplish stain after long immersion in hsematoxylin. 

 The nuclei, on the other hand, are very receptive to the same stain. They 

 are of moderate size, usually rather oval, showing granular contents without 

 any distinct nucleolus. 



