214 DR. W. X. F. WOODLAXD OX THE 



reflected left side of the glandular mass. In diagi'am C the 

 reflected left side of the gas gland has inci-eased so as to extend 

 over the opposite or right side of the gland, a narrow crack 

 (continuous posteriorly with the bladder cavity) only being left 

 l)etween the dorsal and ventral halves of the gas gland. In 

 diagrams B and A, owing to the coalescence of the glandular 

 masses of the dorsal and ventral portions of the gas gland on the 

 right side {i. e. the replacement of the short strip of thin epithelium 

 which in C closed the tube on the right side), the narrow crack 

 (C) becomes bounded on all sides l)y the glandular substance, and 

 this crack narrows anteriorly until it disappears shortly before 

 the gas gland itself terminates. 



The mass of glandular epithelium (PL IX. fig. 68) resembles that 

 of Coris julis in being (apparently) almost devoid of gland lumina. 

 Small intercellular cracks are visible here and there between the 

 cells in my preparations, but that is all to be observed in the inactive 

 gland. On the other hand, the glandular mass is penetrated by 

 capillaries, and the large cells appear to arrange themselves round 

 these capillaries to some extent, giving the gland in section almost 

 a lobulate appearance. The cytoplasm of the cells is conspicuously 

 darkened where in contact with the capillaries. Now and again 

 large cells are found with a very large nucleus, but these are rare. 

 Finally, it may be mentioned that the capillaries of the rete 

 rairabile possess the peculiar endothelium which I have already 

 described in Gobius pagcmellus and found in most " red bodies." 



Pehca fluviatilis. 



The " red body " of the freshwater Perch is a diiTuse organ 

 situated anteriorly on the ventral and lateral portions of the 

 bladder wall (PI. IX. fig. 69). The retia mirabilia ai-e seen as small 

 fan-shaped tufts present at the extremities of the variousbranchings 

 of the closely-associated artery and vein (both included in the 

 red streak seen in the bladder wall), and bordering these tufts of 

 rete are the areas of gas gland. The gas gland is of the ordinary 

 massive type, but feebly developed compared with the gas glands 

 of most marine fish, consisting in its thickest parts of not more 

 than six cell-layers (see text-fig. 62, p. 240) and dwindling to one 

 a.t its edges (PI. IX. fig. 70). The giant cells described by Deineka 

 in young Perch are only of very moderate size in my preparations *, 

 indeed, not so large as those I have figured in the case of Zeus ; as 

 in Zeits, amitosis occurs in connection with most of the cells. 

 With reference to the suggestion of Deineka that these giant cells 

 subdivide into groups of the smaller cells as a consequence of the 

 fragmentation of the nucleus, I have already advanced reasons for 

 regarding this as improbable (see Zetts). 



Previous Desanptions of the Structure of the Ophidium 

 or Third Type of Red Body r 



I shall here merely enumerate the chief histological descriptions 

 of gas glands of the massive type. Emery 1880 (33), Fierasfer ; 

 * My Perch were from 10-14 cm. in length. 



