78 



CAUDAL GILLS OF ZYGOPTERID LARVAE, 



the size of the individual alveoli is smaller. The positions of 



the blood -canals, nerves, 

 and internal lam in??, and 

 the distribution of the 

 ..'}T larger trachese, are very 

 similar in both forms. 

 The branch trachese, how- 

 ever, are moi"e numerous, 

 and come off less oblique- 

 ly from the main stems. 

 Their branchings towards 

 the hypodermis are also 

 of a more dendritic char- 

 Text-fig.lf). acter, as can be seen in 



T.S. through the constriction of the median PI. i., fig.6. In the less 

 gill of Neosticta canescens Tillyard; pigmented parts of the 

 (X233). Lettering as on p. 109. g^]]^ ^^ ^g possible to see 



bundles of capillaries starting out from the somewhat " knobby" 



and deeply pigmented ends of 



the dendritic branches. These 



capillaries seem to run in all 



directions upon the inner border 



of the hypodermis, and their -^y 



general distribution closely re- 

 sembles that seen in the Nodate 



Lamellar type of gill. 



At the constriction, the 



alveolar meshwork is reduced 



to a minimum. The two blood- 

 canals pass through it with their 



inner walls almost in contact^ 



separating the main trachese 



to left and right. A trans. ,^ ,. ,« * 



f Text-fig. 16.* 



verse section through the con- 

 striction in the median gill of Neosticta is shown in Text-fig. 15. 



* T.S. through distal joint of the median gill of Neosticta canescens Till- 

 yard; ( X 130). hm, confluence of the two blood-canals; nv, nerve; other 

 lettering as on p. 109. 



