332 



HISTOLOGY 



situated proximally in their bases (Fig. 296, ep.c.\ One or two of such 

 cells will be found between most lamellae. Any particular function which 



they may possess is unknown. 



Those cells of the basal layer 

 which are reflected over the la- 

 mellae become the true respiratory 

 cells (Fig. 296). In this position 

 they have relinquished the work 

 of desquamation, and consequently 

 remain a simple epithelium. 

 Their renewal, when injured or 

 worn out, is secured by mitotic 

 cell-division in the fundus and on 

 the lower sides of the lamellae, and 

 the moving of the whole layer up 

 to fill the gap. A mitotic figure 

 which is probably fulfilling this 

 duty is shown on the middle side 

 of the lamella in the figure. 



In structure the respiratory 

 cells are decidedly specialized. 

 They do not become so flat and 

 thin as many other cells do under 

 the circumstances, but they broad- 



FiG. 296. Part of a section through the gill 

 filament of a goldfish, res.c., respiratory cells; 

 bl.c., blood cells in the many sections of cap- 

 illaries; ep.c., unmodified outer cells of the 

 stratified epithelium from which the gill is 

 developed (possibly has some obscure glandu- 

 lar function). X 1300. 



en and become lighter, and the 

 cytoplasm becomes far less dense 

 than it is in the lower parts. 



Technic. The gill tissues are 

 very easy to cut in paraffin on ac- 

 count of the delicacy of the vari- 

 ous structures which have to be so because of the necessity of allowing 

 the oxygen to pass through. For the same reason the organs are quite 

 hard to fix without shrinkage and distortion. Flemming's fluid, Zen- 

 ker's fluid, and chrom-aceto-formaldehyde gave good results, especially 

 when allowed to act for a long while. 



LITERATURE 



REISS, A. "Der Bau der Kiemenblatter bei den Knockenfischen," Troschler's Arch.fUr 



Naturges., 47 Jahrgang. 

 OSBORN, H. L. "On the Gill in Some Forms of Prosobranchiate Mollusks," Stud, from 



the Biol. Lab., Johns Hopkins University, Vol. Ill, 1884. 

 MOROFF, TH. "Uber die Entwicklung der Kiemen bei Knockenfischen," Arch. f. mik, 



Anat., Vol. LX, 1902. 



