374 ME. H. M. BERNAED ON THE 



The Tracheal System. — The tracheal tubes of the Galeodidse form a connected system, 

 the segmental origin of which is obscured (PL XXX. fig. 13). 



Erom each stigma of the first pair one large trunk runs forward, another upward, and 

 another backward. The distribution of these need not be described in detail ; it can be 

 o-athered in outline from the figure. It is, however, especially to be noted that the 

 trunk running backward branches and pierces the diapliragm, and, as shown in the 

 figure, is in direct connection wdth the abdominal system. 



The arrangement of the latter and its connection with the stigmata can also be 

 gathered from a comparison of figs. 13, 14, 15 (PI. XXX.). Figures 13 and 14 were 

 recoustructed from both dissections and sections which were made especially to ascertain 

 whether there was any trace of a segmental arrangement, that is, whether there were 

 any remains of special tufts of tracheae in the same transverse planes witli the dorso- 

 ventral muscles. These muscles mark tlie positions of the original inter-diverticular 

 blood-spaces, into which the primitive tracheal invaginations once projected. Although 

 the alimentary canal is now so specialized that these spaces have quite vanished, yet it 

 appeared as if the tracheal tubules which are given off by the main longitudinal 

 trunks on each side of the alimentary canal irregularly along its whole length tended 

 to be rather more thickly grouped at the points where alone they are indicated in 

 fig. 14 *. 



The pericardial trachea {pet) is connected anteriorly by a forked piece with both 

 longitudinal trunks, and in the 2ud segment by a large single trunk from the ti'achca 

 rising from the right stigma {G. arabs). Birula figures it also on the right side for 

 G. ater. In fig. 13 (Pi. XXX.) it is (? wrongly) drawn coming from the left side. 



I have found no trace in Hhax of the aborting trachea in the fourth segment shown 

 in the figures of Galeodes. In other respects the systems of the two genera resemble 

 each other. There is, however, an additional connection in Rhax which is of some 

 interest. It is indicated in fig. 13 (PI. XXX.) in the 1st abdominal segment by dotted 

 lines, and from it one of the branches rising to the pericardial trachea seems to spring. 

 We appear to have here, in the 1st and 2nd segments, remains of two of the original 

 tracheal invaginations which once ran straight vip from the stigmata alongside the 

 dorso-ventral naiscles towards the heart. These presumably aerated the original inter- 

 diverticular blood-passages in their own segments. 



In Bhax, just within the aperture of the two pairs of abdominal stigmata, the thin 

 chitin is strengthened by very beautiful star-like thickenings, which change gradually 

 into the typical hoops (PI. XXX. fig. 19). 



Galeodes is the only Arachnid in which tlic primitive tracheal invagination has 

 developed into these long branching and anastomosing tubes. A study of the figures 

 shows that the Avhole system, though now highly specialized, has been developed from 

 the fusion of a complete series of branching tracheae arising from segmental stigmata, 

 commencing anteriorly in the 4th segment. We found, from our study of the circvilatory 

 systems in Galeodes and Thehjphomis, that we were justified in assuming such a series 

 for the primitive ancestral form. 



* Birula (22) mentions swellings ou the main longitudinal trunk, but they do not appear to be segmentally 

 arranged. 



