\ 



GAS GLANDS OK SOME TIXHOSTKAN FISHES. 205 



no l;n-ge duets compai'a1)]e with those we have seen in the glands 

 consisting of folded epitlielium ; on the contrary, the only ducts 

 visible are narrow slit-like channels occasionally to be detected in 

 their coarse between the cells. These narrow channels vaiy in 

 width greatly according to the state of activity of the gland ; they 

 are necessarily numerous (though by no means always to be 

 observed) in order to provide means of exit to the surface for all 

 the numerous cells concerned, and they open on the gland surface 

 inside the bladder lumen by small pores. Also penetrating the 

 mass of the gland are numerous fine capillaries supplying the 

 individual cells with nuti'iment a,nd oxygen on the sides remote 

 from those facing the ducts just mentioned. All the intracellular 

 structures previously mentioned as occurring in connection with 

 cells of the gas gland are here shown in a very obvious manner. 

 Figure 50 (PI. VI.) shows intrncellularlumina. one in longitudinal 

 section. As to the significance of these intracellular passages found 

 in gas gland cells, it is not necessary to regard them all as possessing 

 purely a nutritive utility as ISTusbaum & E.eis have supposed ; it 

 seems more probable, judging from their appearance in such cases 

 as that illustrated in figure 50, that some at least are concerned 

 with the passage of the gas bubble from the interioi- of the cell 

 to the exterior; they are veiy rare in their occurrence in my 

 preparations and in transverse section closely resemble bubbles, 

 especially if near the nucleus. The whole mass of cells composing 

 the gas gland is therefore penetrated by capillaries and gland 

 liimina. I have not obsei-ved a pancieas in the region of the 

 rete in Ojyhidiitm. 



Other Examples of the Third or Ophidium Type of " Red Bodyr 



Box Boops L. 



The "red body" of Box looj^s has the curious macroscopic 

 appearance shown in figure 51 (PI. VI.). Figure 52 (PI. VIL)isa 

 diagram of a transverse section through the middle of the " i"ed 

 body," and the appearance of two concentric loops is thus seen to be 

 due to the disposition of the rete mirabile. The primary artery 

 and vein enter the " red body " postei'iorly and break up into 

 smaller ai"teries and veins (interiningkd with pancreatic acini) to 

 form the rete mirabile as usual. The glandular epithelium consists, 

 as in Ojyhidium, of a mass of cells interpenetrated by capillaries 

 and lumina, but here the cells are all approximately equal in size 

 and the gas gland is more than a dozen cells thick. 



Atherina hepsetus L. 



In macroscopic apjoearance the " red hoAj" oi Atherina hep)seius 

 is diffuse in form (PI. VI. fig. 53) and consists of tufts of retia 

 mirabilia borne laterally on a median pair of vessels (artery and 

 vein) with cori'esponding tracts of glandular epithelium . The glan- 

 dular epithelium (PI. VII. fig. 54) is very similar to that of Box 

 hoops ; in other words, it consists in its thickest parts of amass of 

 small cells, seven or eight cells in thickness, with inter- and 



