Catostomus macTockeilus, a sucker, and Poecilia reticulata, a livebearer, are subjected to dissimilar mechanical stresses while most of their bony structures are forming. Osteogenesis occurs in the sucker when it is a fiee-living larva, whereas in the livebearer it occurs intrafollicularly. The first-formed bones of both species are those that meet functional demands and are subjected to the greatest stresses. These are the movable bones associated with the acts of respiration and feeding, and some of the axial bones. The cranial roof is the last to calcify. The primary differences in osteogenesis of the two species, such as in the vertebral column and caudal fin, can be correlated with differences in stress. Surface forces on calcifiable tissue perhaps assist in the deposition of calcium salts.

Although suckers are among the commonest of the fresh-water fishes of North America, surprisingly little study has been devoted to their osteology and its remarkable adaptation for suctorial feeding. The most complete description is given by Sagemehl in his 1891 investigations on the cranium of cyprinoid fishes. Since that time, Edwards ('26) has discussed the protractile apparatus of the mouth of catostomid fishes, and Gregory ('33) in his classic work on fish skulls has a short section on catostomids based in part on Edwards' work. Eaton ('35) has comments on the family in a discussion of the evolution of the upper jaw mechanism of fishes. In his study on the bones of the ethmoid region of the fish skull, Starks ('26) has included the catostomids, as has Adams ('40) and Krumholz ('43) in comparative studies of otoliths and Weberian ossicles respectively. Nelson ('48; '49) studied the Weberian apparatus and the opercular series of catostomids specifically. There are also remarks by Ramaswami ('55a; '55b) comparing the sucker skull to some of the cyprinoid fishes he was investigating. No complete study has, however, been made of the skull of suckers.The sucker skull is not only an interesting study in adaptation, but is also of interest in the information it may reveal on the origin and relationship of the eventognathous fishes. MATERIALS AND METHODSThis investigation utilized articulated and disarticulated skulls of mature Catostomus macrocheilus and C. catostomus. The genus may be considered a basic type of catostomid. The descriptions and illustrations are based on C. macrocheilus. There are only a few minor differences between the two species and it is hoped to note these in a future study comparing the osteology of catostomids as a group.Some comparisons were made with skeletal material of Carpiodes carpio, a sucker perhaps more highly modified than Catostomus, and with the squawfish (Ptychocheilus oregonense), a large predaceous member of the closely related cyprinid f amily.2 X-rays of adult suckers were taken and proved of value in orienting the natural position of some of the larger bones. A few alizarin transparencies of juveniles were also made, but the principal reliance for the investigation was on the cleaned skeletons of adults.Fresh and formalin preserved specimens were used to study the jaw musculature.Histological sections of the lips, pharyngeal pad, and cephalic lateral line were stained with hematoxylin-eosin and by Heidenhain's Mallow-azan method. The last gave by far the best differentiation.Unless otherwise specified, the nomenclature for the skull bones is that recently used and up-dated by Harrington ('55). Although his description is for Notropis, a cyprinid, the homology of the bones is not difficult to render. Harrington's work and the series by Ramaswami ('52-55) were frequently referred to. The abbreviations used throughout in the illustrations are also those used by Harrington except where new ones had to be added. These abbreviations should be standardized.The homology and ter...

No abstract

The paddlefish (Polyodon spathula) is one of the most primitive and unique freshwater fishes of North America. It is adapted as a plankton filter-feeder. The wide mouth and greatly expansible pharyngeal cavity allows it to process a large quantity of water. Numerous setiform gillrakers, which operate against the flattened surfaces of the gill arches and opercula, are capable of filtering out small food particles. The abundance of taste buds and mucus secreting cells in the buccal cavity and pharynx probably aids in selecting and entangling the food. The first segment of the stomach is provided with peculiar, large longitudinal rods of fat which may help i n selecting food from water by causing occlusion of the small lumen when the striated fibers of the muscularis contract. Teeth, unnecessary for microphagous fishes, are absent in adults.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. American Society of Ichthyologists and Herpetologists (ASIH)is collaborating with JSTOR to digitize, preserve and extend access to Copeia.