Rectal Traclwal Qills. 213 



II. Material and Methods. 



I took IJhelliila 4-iiiaciilataas the niaterial of the present study, as it is 

 easily obtaitiable in the pools arouiid Sapporo and it has the rectal gills 

 well developed. To fix the material the following niixture ^ was most 

 successful. 



1. , Alcohol absolutiis 6 vol. 

 ) Chloroform 1 vol. 

 j 40P'o Formol I vol. 

 "^ Qlacial acetic acid 0.,S vol. 



2. Picric acid, 1% against the total mixture 1. After immersion 

 for 24 hours or more, the samples were taken out and washed with 90% 

 alcohol, then preserved in alcohol of the same grade. Beside tiiis fluid 

 the following mixture-l was also fouiid good. 



Alcohol absolutus 1 vol. 



Aqua destillata 30 vol. 



407o Formol 6 vol. 



Glacial acetic acid 3 vol. 



The samples fixed with this fluid were washed several times with 

 70% alcohol and preserved in 90° ^ alcohol. 



Both paraffin and celloidin were used in imbedding; and the double 

 staining was done either with Delafield's hämatoxylin and eosin or with 

 the former and Lichtgrün, both of which brought good results. 



III. The Rectal Tracheal Gills in the Last Nymphal 



Stage. 



Relation between the Alimentary Canal and the Tracheal System. 



Concerning the anatomy of the alimentary canal in the nymphal 

 stage of dragonflies extensive studies have been made by several authors, 

 of these I regard the werk by Sadones") as the most painstaking. His 

 material was Libcllula üepressa from Europe as well as an undeter- 

 mined species of Aeschna. The material used by Sadones and by me 

 show, as a whole, a similar structure, although the both are a little different 

 from each other in the minute points in the tracheal gills of rectum as 

 mentioned below. 



In this stage of nymphal life are to be seen three principal divisions 

 of the whole canal wich are subdivided distinctlv as follows. 



'I W. Docters van Lceuwen regarded this mixture as the best for 

 fixation of insect-larvae iZool. Anz. Bd. 32. 1908. p. 316-318). 



-) This mixture is recommended by Bedau in his research on the 

 Compound eyes of water bugs (Zeitschr. f. Wiss. Zool. Bd. XLIX. 191 1 p. 418). 



2) Sadones: La Cellule, Tome XI. 1896. pp. 274-324. 



