ONYCHOPHORA OF WEST AUSTRALIA. 377 



yV oil-immei'sion lens, branched trachese can easily be found 

 (&"ee PI. II. figs. 7 ck 8). 



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

 organs are well supplied with trachete and branching is ea,sily 

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

 to practically living tissues that the full extent of the tracheal 

 system becomes apparent. PL 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 tracheae have so far met with little 

 success. Tliey simply end, but wliether the eiid has been seen 

 or whether still finer capillary tubes continue and penetrate 

 cells is un">known. 



The Structure 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 thickening is easily observed with a modei'ately 

 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 ai'isen as to whether they 

 pressnted the spiral so chax-acteristic of other tracheate arthi^opods. 

 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. jSTo one seems to have gone beyond this 

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

 " Tlie trachea; are minute tubes exhibiting a faint transverse 

 striation which is probably the indication of a spiral fibre." 

 Gaflfron (8) remarks that it is questionable whether a spiral 

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

 only with high powers. 



This question has been solved, like cei'tain others, thi'ough 

 the application of the oil- immersion lens to fresh material 

 mounted in sa,lt solution. There is now no doubt but that the 

 delicate trachea; of Ferijjatoides a,re strengthened by an exces- 

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



The Crural Glands. 



Reference has already been made to the crural glands in the 

 section dealing with the externa] characters. 



They are particularly well developed in the males, wdiei'C 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 botli tlie West Australian forms, the crural glands are enth'ely 

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

 It is situa.ted distally to the nephridia,l a,pertnre on the ventral 

 surfa.ce of all the legs except the 4th and 5th, where the excretory 

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



