ON THE STUDY OF THE SKELETON OF CARASSIUS AURATUS L.

Carassius auralus is one of our commonest fresh-water fishes and hence a good material for a preliminary study of the tdeostean osieology.There are about 373 separable bones in die whole body of C. auraius, of which 201 belong to the axial skeleton, 172 to the appendicular skeleton. Of the axial skeleton, 135 belong to the skull, 32 to the vertebral column, 8 to the Weberian organ, and 26 to the ribs. Besides, there are 989 gill-rakers and 70 intermuscular bones.The shoulder girdle of C. auratus, like that Of many other bony fishes, consists of 12 pairs of separably bones, and is the most complex of any other vertebrates., Jordan pointed out that there is a great confusion in names connected with the shoulder-girdle of fishes. This is due to an attempt to homologize its separable bones with those of the shoulder-girdle of the land vertebrates. In consequence, the terms, such as clavicle, scapula and coracoid, are also used in fishes. In tact, the fishes and the land vertebrates have doubtless sprung from a common stock, related to the crossopterygians of the present day, which was undifferentiated in the details of its shoulder-girdle. From the undifferentiated shoulder girdle, are respectively derived the rather simple shoulder-girdle of the land vertebrates and the most complex shoulder-girdle of the bony fishes. So we must be clear in mind that the shoulder-girdle of the fishes is, in general, homologous with that of the land vertebrates but that this homology does not extend to the details of structure. The bones of the anterior limb of the specialized fish are not by any means identical with the clavicle, scapula, coracoid, humerus, radius, ulna, and carpus of the land vertebrates.The posterior portion of the skull of C. auratus is rather regular. The orbitosphenoid and the intermuscular bones are present in this fish. Its two parietals meet with each other in the median line of the cranium (i.e., they are not separated by the supracccipital). The shoulder-girdle is closely connected with the skull. Its ventral fins are situated on the abdomen. All these conditions indicate that this fish ranks low among the teleosts.Cxrassius auralus chiefly feeds upon silicon algae, filiment algae, water-grasses, and zooplan-kton. As the food particles are rather small, the mouth of the fish docs not need to open widely, and the structures of its skull are also adapted to this condition. The maxillae, palatines, articulars, and quadrates are rather short and small, the interhyals are poorly developed, and the connected points of hyomandibulars are situated near the anterior half of the cranium. All these restrict the mouth to being rather small and unable to open widely. The morphological features, such as the small and toothless mouth, well-developed gill-rakers, toothed pharynx and hard sclerotic plate are all related to the habits of eating.Owing to the fact that the fish can easily secure its foods, the trunk bones do not adapt to quick swimming. The number of the trunk vertebrae is greater than that of the caudal vertebrae. The ventral fins of the fish are situated on its abdomen, and it also has the Weberian organ and the intermuscular bones. Hence, this fish usually swims slowly and floats up and down freely.In conclusion, based on our study of the skeleton of C. auratus, we may easily perceive the soundness of the biological principle that the organism is unified with its living conditions.