E. MAKSIIALLT. — FLAGrXLATED CHAMBER. 129 



occasionally being as long as 275 /<. Those situated in the peri- 

 phery of the clioauosome and adjoining the subdermal cavity 

 are, on the whole, somewhat longer than others in deeper positions. 

 The cross-section is approximately circular, with a diameter of 

 45-90," (about 7-1 /< on an average). 



The cavity within the delicate chamber-wall is always 

 empty, — I mean, perfectly free of trabecula\ The broadly open, 

 truncated end is the so-called apopyle, by which the chambers 

 open into the lacunte of the internal trabecular layer. On nearly 

 the entire external surface they expose themselves directly to the 

 ineurrent lacuna; of the external trabecular layer. Here and 

 there on that surface the fine branched ends of the extei'nal 

 trabecular find their insertion (PI. V, fig. 3(5). 



Sometimes the chamber shows one or more outbulgings on 

 the sides or near tlie outer end, and these may sometimes be so 

 prominently develoj^ed as to bring about the appearance of a 

 lobed chamber. In such cases the wall (reticular membrane) 

 passes without doubt continuously from one lobe into another, 

 making a sharp or a rounded bending. I think these outbulgings 

 or diverticula indicate the process by which the chambers 

 multiply themselves. After reaching a certain stage of develop- 

 ment, the daughter-chambers should become histologically dis- 

 continuous and acquire a certain degree of independence, though 

 remaining side by side and connected together in the manner 

 soon to be described. 



In forming the chamber-layer often alluded to, the fully 

 formed chambers are arranged close together with the apopyles 

 all directed the same way, without however mutually pressing 

 one another at any point. Hence, the chambers as well as the 

 apopyles remain round or roundish in circumference, leaving an 



