Protocerebruni of Micropteryx. 141 



very large cells {cellule maestre) are developed behind and 

 above the protocerebruni, and the fibres from these proceed 

 over the front of the protocerebrum to the ventral brain 

 by way of the oesophageal connections. 



TECHNIQUE. 



I. Fixation and Impregnation. 



My early work on Micropteryx was all done upon material 

 which had been fixed and stained by very simple methods. 

 I became convinced that for insect neurology the employ- 

 ment of complicated technique was not only desirable 

 but necessary. Accordingly I devoted the early spring of 

 1915 to a somewhat extensive series of experiments in 

 staining and fixing the brains of cockroaches (Periplaneta), 

 my object being to familiarise myself with some forms of 

 technique which I proposed to apply later to Micropteryx. 

 I shall describe my methods for both insects together, 

 though some of them are only applicable to one or other 

 of the insects. 



Owing to the chitinous cuticle of insects it is necessary 

 to take every care to ensure the penetration of the fixing fluid. 

 Unless there is good reason to the contrary Micropteryx 

 should be cut in two with a sharp knife ; only the anterior 

 end will be preserved and fixed. A cockroach, on the other 

 hand, should be chloroformed and held between the finger 

 and thmnb, with the head resting on the thumb-nail ; the 

 epicranium should then be punctured with a small sharp 

 kiiife, and also the eyes if the individual is a large one ; 

 the same knife should then be used to remove all the mouth 

 parts and the labrum at one transverse sweep, the thumb- 

 nail forming a block on which the cutting is done. All this 

 can be performed without any damage being done to the 

 brain by pressure. The head is then cut off and placed in 

 the fixing fluid. 



Fixatives. Osmic Acid (osmium tetroxide). — This is 

 perhaps the most generally used of all fixatives, ever since 

 the time of Viallanes, who described it as " le reactif le 

 plus precieux que nous possedions pour mettre en evidence 

 le trajet des fibres.'' It has been used in strengths of from 

 1% to 1%. Flemming's solution has also been much 

 used, and it is probable that its results are slightly better 

 than those given by osmic acid alone. Bottger recom- 

 mended its employment for periods of about three weeks; 



