THE CIRCULATORY AND NERVOUS SYSTEMS OF THE GIANT SCALLOP (PECTEN TENUICOSTATUS, MIGHELS), WITH REMARKS ON THE POSSIBLE ANCESTRY OF THE LAMELLIBRANCHIATA, AND ON A METHOD FOR MAKING SERIES OF ANATOMICAL DRAWINGS

Abstract

Circulatory System.—The large size of the animal makes it possible to inject the vascular system successfully. Blood from the mantle is returned immediately to the heart. Most of the blood from other portions is carried to the kidneys, from which it is carried to the gills, and then back to the heart. A portion may dodge the kidneys and go to the gills. Blood seems to act both as blood and lymph. (See pp. 227-234 and Figs. 3, 4, 5 and 7.) Nervous System.—The cerebral and pedal ganglia are small and somewhat removed from their usual positions. The visceral ganglia are very large and complicated in structure. The circumpallial nerves and the branchial nerves have ganglion cells throughout their length. The otocystic nerves originate directly from the cerebral ganglia. (See pp. 234-239 and Figs. 6, 8, 9 and 10.) Phylogeny.—Ontogeny and the probable conditions that have resulted in the complication of structure, both seem to indicate that the division of the Mollusca into lamellibranchs and gastropods, took place at an early time, before the ancestors had attained much complexity of structure. There seems to be no reason for believing that lamellibranchs ever had more complicated head machinery than they have at the present time. If this is true they probably have never had need of more anterior ganglia than they now generally have. (See pp. 239-243.) Anatomical Drawings.—A combination of photographs and drawings may sometimes save much time and tedious work. (See pp. 243 and 244.)