. The elasmobranch fishes . Fig. 149. Sagittal section through buccal cav- ity of Baia erinacea to show valves (v.).(From Eand.) In the free-swimming sharks the current enters the mouth, from which it passes through the pharynx and into the gill pockets, the external clefts, in- cluding the spiracle, at the same time remaining closed. The mouth then closes, the external clefts open, and the water is forced out. In the rays, which spend most of their time on the bottom and hence often in mud or sand, there is an interesting change in the direction of the current. In these the greater part of th
. The elasmobranch fishes . Fig. 149. Sagittal section through buccal cav- ity of Baia erinacea to show valves (v.).(From Eand.) In the free-swimming sharks the current enters the mouth, from which it passes through the pharynx and into the gill pockets, the external clefts, in- cluding the spiracle, at the same time remaining closed. The mouth then closes, the external clefts open, and the water is forced out. In the rays, which spend most of their time on the bottom and hence often in mud or sand, there is an interesting change in the direction of the current. In these the greater part of the current enters through the spiracle and but little through the mouth. The valve of the spiracle then closes and the water is forced out ventrally through the external branchial clefts. At the expulsion of the water the mouth does not entirely close, but only a little of the current is able to gain exit through it because of valves wdiich are located on its roof and floor (v., tig. 149). In ra^ys there often occurs a rever- sal of the current, by which the water is spouted outward through the spir- acle. Rand (1907) has shown that this may be brought about experi- mentally in several ways. In the first place spouting may be produced by putting the ray into water over- charged with carbon dioxide, or it may be the result of fatigue as is shown by compelling the ray to keep in rapid motion for a period of time. Again, spout- ing may be produced by putting a soft substance, as for example sea moss, into the spiracle. To any of these experiments the ray responds by ejecting a col- umn of water through both spiracles. Rand has shown further that by striking the margin of the spiracle or of the eye on a single side, spouting may be pro- duced by a single spiracle on the side thus irritated. While spouting is characteristic of the rays it is not confined to them. In Squatina, a form which spends much time on the bottom, I have also found spouting to occur. But in this type it is not
Size: 4670px × 1070px
Photo credit: © The Bookworm Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisherberkeleycalifuniversityofcaliforn
