86 



CAUDAL GILlS Of* ZtGOPfERlD LARV^, 



Except at the mid-rib, the cuticle is only of moderate thick 

 ness, about 8-9/x; but nearb 



half of this is usually occupied by 

 the tough outer stratum 

 which stains deeply with 

 eosin. Along the mid-rib, 

 this tough outer stratum 

 becomes twice as thick. 

 Small spines or bristles are 

 arranged regularly along 

 the mid-ribs, as Avell as 

 along the dorsal and ven- 

 tral edges of the gill-blade, 

 right up to its distal end, 

 where, also, a few hairs 

 may be present. 



The hypodermis is pecu- 

 liarly modified in connec- 

 tion with the narrowing of 

 the interior of the gill and 

 the elimination of the al- 

 veolar tissue. Many of 

 the cells become columnar 

 or even spindle-shaped, 

 standing up clearly and 

 separately between the 

 cuticle and the inner base- 

 ment-membrane ; in such 

 cases, the long axes of the 

 nuclei lie at right angles 

 to the cuticle instead of 

 being parallel with it. 

 8ome of the columnar or 

 spindle-shaped cells may be as much as SO/jr. in height, but they 

 are much narrower than the ordinary flattened cells, and much 



"Ideal (semi -diagrammatic) T.S. across the Vertical Lamellar Gill-system 

 of Anstrolestes (Lestkl Form of Gill) to show the internal structure of the 

 gills. Lettering as on p. 109. 



mr 



