PETUOMYZOX .■\lAKIXrs. l.o;3 



and the now teetli are already formed when the old ones are lost. The moulh 

 shuts laterally instead of verticall}'. 



The seven g-ill-apertures are scarcely separated from each other by the 

 width of an orbital diameter, and each is margined in front by a membranous 

 fold, and defended posteriorly by papillae ; and there are two valves behind, 

 which meet like folding doors. These gill sacs open into a longitudinal 

 canal, which is below the oesophagus; it terminates posteriorly above the 

 pericardium, and oj^ens in front into the gullet by a valve like a glottis. An 

 artery runs between each pair of gill sacs, so that each sac receives branches 

 from two arteries, like the gills of osseous fishes. The water for respiration 

 may either be taken by the mouth, or by the gill-apertures when the animal 

 is attached. Dumeril describes a gland between the buccal disc and the 

 respiratory cage, which is enveloped in a strong muscle, and contains a 

 yellow, or yellowish-brown, thick, acid fluid. The excretory duct opens into 

 the mouth. It is regarded by some observers as the salivary gland. 



The first dorsal fin begins behind the middle of the body; its base exceeds 

 the length of the head. It is divided from the second dorsal by a distinct 

 interspace. The second dorsal has a long triangular form ; it increases in 

 height to a point, and is then as high as the tail beneath it is deep ; the 

 height then declines towards the caudal fin, with which it is conHuent. 

 The caudal fin is small, rounded at its extremity, and extends symmetrically 

 on both sides of the termination of the vertebral column. In the position of 

 the anal fin there is sometimes a membranous ridge jirolonging the caudal iin 

 to the vent. The vent is one-quarter of the length of the fish from the ex- 

 tremity of the tail, and has a short longitudinal opening, which shows the 

 urogenital papilla. 



The cephalic mucus-canals are well-developed. There is a row of pores 

 above and behind each eye, and another row below the eye, which is }u-olonged 

 to the lip, and there are other rows of pores over the gill-apertures, becoming 

 irregular on the back and sides; there are also rows on the throat. The body 

 is always very slimy. 



The colour of the back and sides varies with locality and season, 

 but is usually grey or some tint of yellow, spotted or clouded with br(nvn or 

 black. 



At spawning-time in the spring, a crest, comparable to that of the water 

 salamander, is developed on the back, between the neck and the first dorsal 

 fin, and on the under side of the body, between the vent and the caudal 

 fin. The ovaries are very large. The fishes excavate furrows on the river 

 bed, by removing stones, which are lifted by suctorial action of the mouth ; 

 and the male and female are said bv .Tanline to moor themselves to stones 



