OXYCHOPHOllA OF WEST AUSTRALIA. 



377 



yV oil -immersion lens, branched tracheae can easily be found 

 (s^ee PI. II. figs. 7 & 8). 



The nerve- cords, ganglia, alimentary canal, and in fact all the 

 organs are well supplied with tracheae and branching is easily 

 discovered. J3ut it is only when an oil-immersion lens is applied 

 to practically living tissues that the full extent of the tracheal 

 system becomes apparent. PI. II. fig. 8 shows more distinctly 

 the manner of division of the tracheal vessels. 



PI. II. fig. 7 is but a very small area of the alimentary canal- 

 wall indicating the course taken by the branching tracheal vessels 

 there. Attempts to follow out with certainty the fine termi- 

 nations of the branched trachec'e have so fur met with little 

 success. They simply end, but wliether the end has been seen 

 or whether still finer capillary tubes continue and penetrate 

 cells is unknown. 



The Structitre of the Trachece. — Typical insect tracheae are 

 elastic structures lined by an extremely delicate chitin layer 

 which is strengthened by a spiral fibre. The spiral fibre is said 

 to be absent from the fine capillary twigs. In large insect 

 tracheae the spiral tliickening is easily observed with a moderately 

 low power of the microscope. The largest tracheae of Peripatus 

 are, however, of minute dimensions, and it is not surprising 

 therefore that uncertainty should have arisen as to whether they 

 pres;ni*'e 1 the spiral so characteristic of other tracheate arthropods. 

 Balfour noticed something and was led to state that the trachea? 

 exhibited a faint transverse striation which he took to be indica- 

 tive of a spiral fibre. No one seems to have gone beyond this 

 since, and Sedgwick (10) in 1910 restated it in tlie description : 

 " Tlie trachea? are minute tubes exhibitino- a faint transverse 



o 



stri<ttion which is probably the indication of a spiral fibre." 

 Gafi'ron (8) remarks that it is f|uestionable whether a spiral 

 fibre exists, the only indication being some fine cross striping seen 

 only with high powers. 



This question has been solved, like certain others, througli 

 the application of the oil -immersion lens to fresh material 

 mounted in salt solution. There is now no doubt but tliat the 

 delicate trachea? of Feripatokles are strengthened by an exces- 

 sively minute but perfect spiral fibre (PI. II. fig. 9). 



TuE Crural Glands. 



Reference has already been made to the crural glands in the 

 section dealing with the external characters. 



They are particula.rly well developed in the males, where a pair 

 can be found for every pair of leg"^. With the exception of the 

 glands of the first and last pairs of legs, which are highly modified 

 in both the West Australian forms, the crural glands are entirely 

 contained in the legs. The external aperture is very distinct. 

 It is situated distally to the nephridial aperture on the ventral 

 surface of all the legs except the 4th and 5th, where the excretory 

 opening is found near the end of the appendage. The extremity 



