ME. H. M. BEENAED ON THE CHEENETIDiE. 425 



in keeping with the view that at one time there were tracheal 

 invaginations in every segment. 



(d) Their position enables thorn to dispense with protective 

 stigmata. The operculum forms an effective covering for them 

 as well as for the genital opening. 



(e) The air-chambers, described and figured in this paper, 

 render the respiratory function o£ the invagination, in this case 

 at least, almost unquestionable. 



These five arguments, I think, completely justify Croneberg in 

 homologizlng these organs with tracheae. Further, in addition 

 to these arguments in favour of their being tracheae, we have 

 the following arguments against their being connected with 

 reproduction : — 



(/) The entire absence of muscles renders it very improbable 

 that they are transmitters of sperm. 



((/) I could find no such close connection between their 

 apertures and the median genital aperture as to warrant my 

 thinking that sperm, on being discharged from the latter, would 

 find its way up into these tubes. 



(h) The only reproductive organs which it seems probable 

 that they might be would be receptacula seminis, but they are 

 said to be confined to the males. 



Summing up these arguments, I think the balance of the 

 evidence is in favour of their being tracheae, and if their claim 

 to serve as accessory reproductive organs is not altogether 

 without foundation, yet, in the case described and figured in this 

 paper, the function of the organs is clearly and exclusively 

 respiratory ; I say " exclusively " because respiration is a some- 

 what exclusive function, at least it certainly would not admit of 

 the air-passages being choked up with sperm-cells. 



It seems to me that we may here have to do with one of the 

 simplest of all known tracheal invaginations, — a short bliud 

 chitinous tube, without highly specialized crenulations, and 

 without specialized apparatus for the protection of the orifice. 

 Some such chitinous invagination must have been the orifinal 

 starting-point of all the more specialized forms, the lung-books 

 tracheal tufts, and tracheae. Further, the formation of the 

 chambers, which appear to be chitin-lined spaces within the 

 original secreting cells, seems to show how the difl'erent speciali- 

 zations of tracheso arose. "By the flattening of such chambers 



LiNsr. jOL'Eisr.— zooLoar, TOL. xxir. 33 



