NOTES. 445 



vain, for years, for Apus in spots where it had previously been found in 

 swarms. The best method of filling up this gap in our Icnowledge will 

 be the transmission of mud, with exaot information as to the place 

 where it was collected, to scientific experts, as to Professor Von Siebold 

 at Munich or Professor Brauer at Vienna ; and by this means the amount 

 of material in the form of animals for investigation will also be in- 

 creased in a considerable and very desirable degree. 



CHAPTER VI. 



Ifote 79, page 178. It was Leydig, the founder of all truly scientific 

 — that is to say comparative — histology, who first pointed out that 

 excessively fine ramifications from the tracheae traverse every portion 

 of the body of insects and lie between all their constituent parts. He 

 shovved that even in the eye, in the ganglia of the brain, and in many 

 glands, &c., tracheae are to be found between the cells of the organs, 

 that they constantly lie quite close to them and not unfrequently end 

 in a peculiar manner. Thus Leydig first discovered the vesicular ends 

 of the trachese among the constituent parts of the dioptric apparatus 

 of the fly, in the crystalline spheres. Even the cells of the fatty tissue 

 ^on the presence of which the survival of many insect-larv^ through 

 the winter seems to depend — are in direct connection with the tips of 

 the tracheae. 



Note %0,pagc 179. From what is stated in the text it might seem 

 to follow that the distinction between arterial and venous blood can- 

 not exist in Insects, which breathe by tracheae, since by that mode of 

 respiration the air is distributed to every part, and consequently the 

 afferent and efferent vessels may contain blood which in each is equally 

 rich in oxygen. It must not, however, be forgotten that even in Mam- 

 malia the difference between the two kinds of blood — the highly oxy- 

 genated arterial blood and the poorly oxygenated venous blood— is 

 essentially occasioned solely by the absolute, or relative, localisation 

 of the function of respiration in organs especially fitted for it — the 

 gills and lungs. Thus, if in insects also there should be organs whose 

 sole task it was to extract more oxygen from the trachese than other 

 parts could, or — when the respiration is effected by water— could 

 depofit it more abundantly in the tracheae at one place than another, 

 such arrangements would certainly contribute to make the blood richer 

 in oxygenated particles in such spots than elsewhere ; and hence, if we 



