420 
bulletin of the bureau of fisheries. 
The grooves which lie between the ridges just described are not filamentous in 
structure but are lined by a continuous finely ciliated epithelium, below which there is 
a large crescent shaped rod of chitinous material for giving rigidity and elastisity to the 
gill. (Fig. 3, c.) Running along the floor of each groove within the cavity of the gill 
there is a large blood vessel. Each is connected with the similar vessels which lie next 
a 
Fig. 3. — Transverse section of gill highly magnified, a, Modified filament containing glands; b, vascular 
interlamellar connective; c, chitinous supporting rod; d, large blood vessel; e, epithelium; /, filaments; 
m, muscles; n, nerves. 
to it, at regular intervals, by smaller tubes which are the interfilamentar connectives 
already described as binding the filaments together. All of these structures are hollow 
and the cavities of all are in open communication. Thus when blood enters the gill it 
penetrates every part, including the filaments and interfilamentar connectives. (Fig. 4.) 
It is common to regard the structures which occur between two folds of the lamella as 
