ANATOMY OF NAUTILUS POMPILIUS. 39 



men ; but its aperture appeared to communicate quite freely with 

 the posterior division of the fifth chamber. 



Four sets of brownish, glandular-looking bodies depend into the 

 anterior division of the fifth chamber, from parts of the delicate 

 septa dividing this from the four small sacs, corresponding with 

 the insertions of the glandular bodies above described. 



In fact, on distending the vena cava with air, it is found that 

 the four branchial arteries traverse these septa, and that the ap- 

 pendages in question are diverticula of their walls. Consequently 

 the anterior wall of each branchial vein is produced into two 

 glandular appendages, which hang into one of the four smaller 

 sacs, while the posterior wall is produced into a single mass of 

 appendages, which hangs into the anterior division of the fifth 

 chamber. 



Although, as I believe, the five chambers do not communicate 

 directly, all the appendages must nevertheless be equally bathed 

 with sea-water, which enters by the apertures of the chambers. 



An impacted yellowish-white concretionary matter filled the 

 anterior chamber ; and a small quantity of it lay as a fine powder 

 at the bottom of the posterior one. In the latter, however, its 

 presence might, by possibility, have been accidental. My col- 

 league. Dr. Percy, who kindly undertook to examine this sub- 

 stance, informs me that he has been unable to detect uric acid 

 in it. The follicular appendages of the branchial arteries present 

 remarkable differences in their external appearance. The eight 

 which hang into the four anterior chambers are similar, slightly 

 festooned, but otherwise simple lamellae; while the four which 

 depend into the posterior chambers are produced into a number 

 of papillary processes. This external difference is obvious enough : 

 whether it be accompanied by a corresponding discrepancy in 

 minute structure I am unable to say ; for I have not as yet been 

 able to arrive at any satisfactory results from the microscopic 

 examination of the altered tissues, and, as will be seen below, 

 the only observer who has had the opportunity of examining the 

 Nautilus in the fresh state has not noted any difference of struc- 

 ture in the two sets of follicles. 



One is naturally led to seek among other moUusks for a struc- 

 ture analogous to the vast posterior aquiferous chamber of the 

 Nautilus ; and it appears to me that something quite similar is 

 offered by the Ascidioida and the Brachiopoda. In both cases, 

 the viscera, inclosed within a delicate tissue, project into a large 

 cavity communicating freely with the exterior by the cloacal aper- 



