750 mr. j. wood-mason on the [June IS, 



ones which follow upon the fine-ringed constricted portion become 

 suddenly still coarser and more prominent and convex, have lost 

 their typical bevelled form, and are separated from one another by 

 far longer and subequal membranous intervals. These are thin and 

 transparent, and each is so constricted in the middle that any two 

 consecutive rings form, with the membrane that connects them, a 

 short hourglass-shaped figure. Six or seven coarsish rings, sepa- 

 rated by much narrower membranous intervals, but otherwise un- 

 modified, complete this portion of the tube, which is twisted spirally 

 to the left, carrying spirally entwined with it the elongated sterno- 

 tracheal muscles. The rings have come to be bent, and, instead 

 of appearing as regular parallel bands as in other parts of the column, 

 to be arranged obliquely, by adaptation, no doubt, to the spiral form 

 taken by the tube whenever it is extended, so as, in fact, to present 

 somewhat the appearance of having resulted from the breaking up 

 into rings of what was primitively a hard spiral thickening of the 

 walls of a membranous tube. Inside the thorax the spiral is neces- 

 sarily very open, from the tube being restricted to a middle position 

 by the membranous bands which sling it, together with the anterior 

 moieties of its great contractor muscles, from the dorsal wall of the 

 body, so as to form a sheath for it ; whilst outside, in the neck, 

 where is more room and more lateral freedom, it becomes closer, 

 there constituting the well-marked superficial loop, the concave cur- 

 vature of which is the true ventral surface of that fine-ringed portion 

 of the tube over which the muscles spread, twisted out of its natural 

 position. 



If an adult female be killed with chloroform and rapidly opened, 

 the sterno-tracheal muscles may be seen slowly to contract, and 

 thereby gradually to take out the superficial spiral "turn" from the 

 trachea, and the intrathoracic rings of this to close up, until at last 

 all that remains of the loop is a slight sinuosity visible near the 

 point where the tube passes into the thorax, the constricted and 

 close-ringed portion, which occupied that position in the unmodified 

 trachea, also having acquired an ineffaceable crook. 



Unfortunately, we possess no more complete description of the 

 highly convoluted trachea of the Australian species than that quoted 

 above ; but the two species R. capensis and R. australis are so very 

 closely allied that we may feel tolerably confident that the tracheal 

 modification is of the same kind in the two, only carried to a much 

 greater extent in the latter, the constricted many-ringed part of the 

 trachea of the former containing two or three potential convolutions. 



In conclusion, I have to thank Col. Godwin- Austen for aid 

 rendered to me in the matter of the illustrations. 



EXPLANATION OF PLATE XLVII. 



Fig. 1. The complete trachea of an adult female of Ehynchaa capensis, nat. 

 size, showing the modified intrathoracic portion of the tube in an 

 expanded condition. The compound three-way piece is seen to be 

 formed by the partial fusion of the last tracheal ring with the modi- 

 fied first pairs of bronchial half-rings; these havo their ventral ends 



