Internal Anatomy of Uropoda Krameri. By A. D. Michael. 15 



the tracheae is similar to that of the same organs in the Oribatidse, 

 although the number of tracheae is far larger, and each trachea much 

 finer, in the Uropoda than in the Orihatidx, but it is not always nor, 

 I think, usually, found in the Qamasidte. I have not examined any 

 large number of species belonging to this family, for the purpose of 

 ascertaining this point, but certainly in Dermanyssus, the tracheae, 

 although not branching so frequently as they usually do in insects, 

 do branch in a very clear and decided manner, sometimes dichoto- 

 mously, sometimes into three branches, and almost always enlarge so as 

 to form a slight swelling immediately before branching. Herr 

 Winkler expressly notices the branching of the tracheae in the genus 

 Gamasus, which agrees with the cases where I have noticed the 

 tracheal system in the same species. Herr Winkler does not mention 

 the unb ranched condition in Uropoda, probably he did not examine it 

 for that purpose, or else his species differs from mine. 



The tracheae of Uropoda Krameri, when they start from the end of 

 the tracheal trunk, are in three bundles (ht), one of which is directed 

 forward, one backward, and one across the body. Each bundle might 

 easily be mistaken for a single trachea, but if a bundle be lifted up 

 with a hair and allowed to fall on a minute drop of water then all 

 the tracheas will float and spread out, and the whole will present the 

 appearance of a skein of floss-silk which has been separated by a puff 

 of wind. Of course the bundles finally separate and supply the 

 various parts of the body. 



The walls of the tracheae are extremely delicate. I have not 

 been able to trace any spiral filament or thickening merely by looking 

 at the tracheae, but probably some kind of spiral structure might be 

 demonstrated by other methods. 



The Brain, or (Esophageal Ganglia. Fig. 20. 



As is usual in the Aearina, the great ganglia in Uropoda are 

 round the oesophagus. A very large supra- oesophageal ganglion (the 

 so-called brain in the Aearina) lies immediately above the oesophagus 

 near where it enters the ventriculus ; this " brain " is compressed 

 dorso-ventrally, and has a somewhat convex anterior margin which is 

 considerably wider than the hind margin. From under the edge of the 

 supra-oesophageal ganglion a very wide commissure runs perpen- 

 dicularly downward on each side of the oesophagus, and joins a sub- 

 oesophageal ganglion which is large, but considerably smaller than the 

 supra-oesophageal ganglion. These ganglia and commissures are so 

 substantial, and so closely joined together, that they form a solid 

 collar round the oesophagus, the commissures, if commissures they be, 

 not being distinctly difierentiated, and with care the oesophagus may 

 be pulled out from the centre of the nervous collar, which then shows 

 a distinct and well-defined hole, or tunnel, through which the 

 oesophagus passed. 



